Persuasive speech

Aggressive and Violent Behavior Among Military Personnel Deployed to Iraq and

Afghanistan: Prevalence and Link With Deployment and Combat Exposure

Deirdre MacManus*, Roberto Rona, Hannah Dickson, Greta Somaini, Nicola Fear, and

Simon Wessely

* Correspondence to Dr. Deirdre MacManus, Department of Forensic and Neurodevelopmental Sciences, Institute of Psychiatry, King’s College

London, De Crespigny Park, Denmark Hill, London SE5 8AF, United Kingdom (e-mail: [email protected]).

Accepted for publication September 11, 2014.

A systematic review and meta-analyses were conducted on studies of the prevalence of aggressive and violent

behavior, as well as of violent offenses and convictions, amongmilitary personnel following deployment to Iraq and/

or Afghanistan; the relationship with deployment and combat exposure; and the role that mental health problems,

such as post-traumatic stress disorder (PTSD), have on the pathway between deployment and combat to violence.

Seventeen studies published between January 1, 2001, and February 12, 2014, in the United States and the United

Kingdom met the inclusion criteria. Despite methodological differences across studies, aggressive behavior was

found to be prevalent among serving and formerly serving personnel, with pooled estimates of 10% (95% confidence

interval (CI): 1, 20) for physical assault and 29% (95%CI: 25, 36) for all types of physical aggression in the last month,

and worthy of further exploration. In both countries, rates were increased among combat-exposed, formerly serving

personnel. The majority of studies suggested a small-to-moderate association between combat exposure and post-

deployment physical aggression and violence, with a pooled estimate of theweighted odds ratio = 3.24 (95%CI: 2.75,

3.82), with several studies finding that violence increased with intensity and frequency of exposure to combat trau-

mas. The review’s findings support the mediating role of PTSD between combat and postdeployment violence and

the importance of alcohol, especially if comorbid with PTSD.

aggression; alcohol; combat; deployment; military; post-traumatic stress disorder; violence

Abbreviations: CI, confidence interval; PTSD, post-traumatic stress disorder.

INTRODUCTION

History tells us that concern about violent offenses among
military personnel returned from deployment is not a new
phenomenon. The idea that war veterans could be so brutal-
ized by their experience of combat as to become predisposed
toward violent behavior on return from deployment was pro-
posed in the immediate aftermath of World War I (1). An out-
break of serious crime in the United Kingdom in 1919 was
attributed to the return of “callous” and “battle-hardened”
former servicemen. Crime statistics showing a rise in violent
crime following the end of World War II reinforced the con-
nection between combat veterans and violence in the minds
of the public, press, and policy makers (2). However, the kind
of epidemiologic longitudinal data necessary to establish any
causal connection was largely not available at the time.
Fast forward to the last 10 years, when the United States,

United Kingdom, and other coalition partners have been

engaged in combat in 2 operational theaters, Iraq and Afghan-
istan. These conflicts have triggered renewed media, politi-
cal, and public scrutiny of the impact of deployment on the
physical and mental health of military personnel involved in
these operations (3, 4). There have been media claims of in-
creased rates of aggression and violent offenses postdeploy-
ment (5–8). Both the United States and the United Kingdom
have published comprehensive government statistics on in-
carceration, and both report, perhaps to some people’s sur-
prise, that, overall, formerly serving personnel tend to be
less likely than the general population to be in prison. How-
ever, in both the United States and the United Kingdom, they
are overrepresented among those imprisoned for violent and
sexual offences (9–14). However, incarcerations are only a
small percentage of total convictions, and total convictions
are likewise only a small percentage of all violent and/or anti-
social behaviors. We must, therefore, look for empirical evi-
dence to support or refute these claims that military personnel

196 Epidemiol Rev 2015;37:196–212

Epidemiologic Reviews

© The Author 2015. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health.

All rights reserved. For permissions, please e-mail: [email protected]

Vol. 37, 2015

DOI: 10.1093/epirev/mxu006

Advance Access publication:

January 22, 2015

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who have been deployed to Iraq and Afghanistan are at in-
creased risk for not just incarceration for violent offenses
but also for convictions for violence and engaging in aggres-
sive and violent behavior.

There are multiple potential factors that may contribute to
the relationship between combat and subsequent violence. It
may be explained by preexisting tendencies to aggressive or
risk-taking behavior such that, irrespective of experiences in
the military or on deployment, an individual would have been
on a trajectory toward violence. Military training and culture,
as well as difficulty readjusting following exposure to threat-
ening and violent operational environments, may also play
important roles (15). Research evidence has accumulated
suggesting adverse effects of deployment and combat during
these conflicts on the mental health of military personnel
(16–19), especially post-traumatic stress disorder (PTSD)
(18, 20, 21) and alcohol misuse (22, 23). Another objective
is therefore to look at the links between offending behaviors
and such mental health problems in those who have returned
from deployment.

What do we know from pre-Iraq and Afghanistan studies

into postdeployment violence?

A substantial amount of research into violence among
combat veterans has been carried out in the United States,
much of which has utilized data from past conflicts, such as
the VietnamWar or the 1991 GulfWar. The results have been
mixed. A number of these studies found an association be-
tween combat exposure (rather than deployment) and physi-
cal aggression, intimate partner violence, and incarceration
postdeployment (24–30). Other studies did not find that com-
bat exposure predicted violence postdeployment (31), and
some found premilitary characteristics to be the strongest
risk factor for postdeployment violence (32, 33). Most stud-
ies from the pre-Iraq/Afghanistan eras proposed that PTSD
was the most important mediator in the association between
combat (trauma) and violent behavior (34–37). Angry re-
actions and irritability have long been recognized features
of PTSD so much so that the Diagnostic and Statistical Man-
ual of Mental Disorders, Fifth Edition (DSM-V), now explic-
itly includes “irritable behavior and angry outbursts” as well
as “reckless or self-destructive behavior,” thus formally ac-
knowledging the evidence for the link between PTSD and ag-
gression (38). Other psychopathologies can, however, also be
linked with postdeployment violence, in particular alcohol
misuse (39, 40).

Weaknesses in past research

A major problem inherent in many of these pre-Iraq/
Afghanistan era studies is that they were carried out many
years after the deployment in question and, given that they
often used self-report measures, this delay increased the po-
tential for recall bias regarding deployment experiences and
the violence outcome. The association with deployment be-
comes increasingly blurred over time, and the reporting of
past experiences can be affected by more recent influences,
such as current health status. Additionally, it should not be as-
sumed that previous conflicts provide a blueprint for the recent

conflicts (41). Each conflict has its own particular character-
istics and, hence, consequences.Different enlistmentmethods
(the US military during the Vietnam War was a mixture of a
conscript and volunteer force; now it is all volunteer, as in the
United Kingdom) would suggest that different military co-
horts are not comparable with respect to predeployment and
sociodemographic characteristics, possibly leading to varia-
tions in postdeployment adjustment problems (42).

Terminology

Research in this area has explored a range of interrelated
outcomes of “violence” and “aggression” and related phe-
nomena. Some studies ask about concerns about aggressive
or violent behavior, and others focus on actual aggressive be-
havior, although that ranges from verbal and property aggres-
sion to threats of violence and actual physical violence. The
term “violence” has been used to refer to anything from hit-
ting and slapping to use of a weapon, grievous bodily harm,
and homicide. Some studies distinguish between the levels of
severity and others do not. Violence may be further divided
into general interpersonal violence or violence toward a fam-
ily member or partner (intimate partner violence). Finally,
more recent studies have looked at criminal convictions and
incarceration for violence as objective outcome measures.
The outcome measurement period also varies from study to
study. We must be aware of these differences when trying to
compare or to contrast the findings from different studies.

Aims and objectives

This paper aims to systematically review studies of the
prevalence of aggressive and violent behavior, as well as of
violent offenses and convictions, among military personnel
following deployment to Iraq and Afghanistan; its relation-
ship with deployment and combat exposure; and the role that
postdeployment mental health problems, such as PTSD, have
on the pathway between deployment and combat to violence.

METHODS

We usedMEDLINE, PsycINFO,Web of Science, and Em-
base to search peer-reviewed journals (from January 1, 2001,
to February 12, 2014) for articles describing the prevalence
of or empirical relationships between risk factors and post-
deployment violence among military populations. Boolean
operators (e.g., AND, OR) and wildcard symbols (e.g., *) were
used in the following key search terms: violen*, aggressi*,
conviction, arrest, incarceration, intimate partner violence,
domestic violence, spousal abuse OR antisocial AND veteran,
military, army, armed forces, navy,marine*, air force, soldier,
reserve* OR national guard AND combat, deploy*, conflict,
war OR operation. We also utilized references from articles to
identify studies. Review articles were also used to identify lit-
erature. Duplicate papers were removed, and the reference
lists of all eligible studies were checked for additional studies
(refer to Figure 1 for detailed results of the search strategy).

Included were quantitative studies that 1) operationalized
violence and/or aggression as actual physical harm caused
by one person against another, a range of aggressive behaviors

Aggression Among Deployed Military Personnel 197

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(property and physical aggression and threat of violence), of-
fending behavior classified as violent, or incarceration for the
latter and 2) explored such behaviors among serving or for-
merly serving military personnel who had been in Iraq or Af-
ghanistan post-2001. Excluded from the current review were
book chapters, dissertations, case studies, papers published
before 2001, qualitative or nonempirical studies, intervention
studies, studies reporting a sample size less than 100, and ar-
ticles not in English. Studies concerning conflicts other than
Iraq and Afghanistan post-2001, such as Vietnam, the first
Gulf War, or the interventions in the former Yugoslavia
were not considered.
This process yielded 17 papers that specifically described

the prevalence of aggressive or violent behavior and/or sta-
tistical relationships between aggressive or violent behavior

and risk factors (Figure 1). Data extraction was conducted
by one researcher (D. M.) and checked by a second data re-
viewer (G. S.). The data collected from each study included
study location, study design, number of service members
evaluated, main variables of interest (deployment, combat
role, specific combat exposure, PTSD or other postdeploy-
ment mental health or behavior problem), outcome measure
of aggression or violence, and measures of effect (Table 1).
The review assessed the quality of the eligible papers uti-

lizing standard critical appraisal guidelines (43). The findings
of all the studies are summarized qualitatively, and issues of
quality are discussed as final conclusions from the review are
drawn.
Studies were reviewed in order to compare characteris-

tics, methods, and findings to determine the feasibility of

Articles Identified Through
Database Searching and

Reading Lists
(n = 224)

111 Duplicates Removed

Abstracts Screened
(n = 113)

Articles Excluded
(n = 72)

32 studies not related to Iraq or
Afghanistan veterans

7 studies related to victims of
violence rather than
perpetrators

4 book chapters
9 review or commentary pieces
2 letters
6 qualitative studies

11 treatment/Intervention studies

Full-Text Articles
Assessed for Eligibility

(n = 41)

Full-Text Articles Removed
(n = 24)

12 papers did not measure
aggression or violence
specifically

11 papers were not on Iraq or
Afghanistan veterans

1 paper was a study of violent
crime data from media reports

Studies Included in
Review
(n = 17)

Figure 1. Flow diagram illustrating the retrieval, selection, and exclusion of articles.

198 MacManus et al.

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completing a quantitative synthesis (i.e., meta-analysis) by
exploring the completeness andmethods of reporting of results
and the homogeneity of the outcomes measured. Where a
meta-analysis was appropriate, we estimated pooled preva-
lence with 95% confidence intervals using a random effects
model that allowed us to assess heterogeneity between studies
based on I2 statistics. Heterogeneity was categorized as low,
moderate, or high on the basis of I2 values of 25%, 50%,
and 75%, respectively. Because of the differences in types of
aggressionmeasured by each study, it was concluded that stud-
ies with prevalence rates for all types of aggression (undiffer-
entiated) would be pooled together and that those with more
similar measures of a specific type of aggression, such as fight-
ing or hitting someone, would be pooled separately. We also
carried out subgroup analyses of studies using similar period
prevalence measures. We explored the feasibility of conduct-
ing a meta-analysis of the studies that explored the association
between combat exposure and aggressive or violent behavior.
As above, where possible, we proceeded with a meta-analysis.

Because of the relatively small number of studies included
in both meta-analyses, it was not possible to explore sources
of heterogeneity. Potential publication bias was also not ex-
amined as the power of funnel plot and statistical methods to
detect publication bias in meta-analyses with less than 10
studies is limited (44). Meta-analyses were conducted by
using the STATA 11 statistical package (StataCorp LP, Col-
lege Station, Texas).

RESULTS

A total of 17 studies from the United States and the United
Kingdom were reviewed: 1 descriptive study, 1 clinical se-
ries, 8 cross-sectional studies, and 7 longitudinal studies. A
summary description of each of the studies is shown in
Table 1; 13of the studies exploredonlygeneral aggression and
violence, 3 studies specifically investigated family or partner/
spousal aggression and violence, and 1 study explored both
family and stranger aggression and violence.

General violence

Self-reported aggression and violence: descriptive study.
In a study from the Walter Reid Institute of Army Research
of 6 specific combat brigade units, 18,305 US soldiers were
surveyed 3 and 12 months postdeployment in Iraq by using a
nonanonymous questionnaire survey (Table 1) (19). Eighteen
percent reported getting into a fight and hitting the person in
the last month, with no significant difference between 3 and
12 months postdeployment follow-up. This study could po-
tentially have underestimated the reporting of its outcome by
the nonanonymous nature of the questionnaire (45), although
this is a common limitation of studies in this area. This report
did not examine the risk factors associated with aggressive or
violent behavior nor did it compare the rates it found among
deployed troops with the rates among nondeployed troops.

Self-reported aggression and violence: cross-sectional
studies. Many of the studies that look at aggression and vi-
olence postdeployment were cross-sectional in design and used
self-report outcome measures. Self-report measures are gen-
erally thought to underestimate the prevalence of aggressive

or violent behavior, especially if a nonanonymous question-
naire is also used. However, the assessment of criminal his-
tory by use of self-report measures has been shown to have
acceptable reliability (test-retest correlations ofQ = 0.80) and
acceptable-to-high validity (46, 47). Cross-sectional studies
are also limited as causal interpretations can not be drawn
from the results.

Hellmuth et al. (48) examined aggression among 359 US
Iraq and Afghanistan combat veterans who had presented to a
Department of Veterans Affairs health-care clinic for physi-
cal or mental health problems (Table 1): 31.8% reported
at least one act of physically aggressive behavior in the past
4 months, 27.7% reported less severe physical aggression
(i.e., threatening without a weapon), and 18.9% reported
more severe physical aggression (i.e., physical fight). They
did not look specifically at the link with deployment or
combat exposure. In a nonanonymous, questionnaire-based,
cross-sectional study of 1,543 US Marines enlisted in the
US Armed Forces who had been deployed to Iraq or Afghan-
istan between 2002 and 2007, Booth-Kewley et al. (49)
showed that 23% of this sample of combat-exposed Marines
scored “high” on antisocial behavior. Combat exposure
was positively associated with antisocial behavior after ad-
justment for a range of demographic and military confound-
ers (Table 1).

Gallaway et al. (50) looked at a nonrandom sample of ac-
tive duty US Army soldiers in Colorado. They reported the
prevalence of self-reported physical aggression in the last
12 months (using questions from the physical assault sub-
scale of the Revised Conflict Tactics Scale (51) excluding
deployment-related aggression) at 6 months following return
from deployment and the factors associated with lower and
higher levels of aggression. Twenty-two percent of the sol-
diers reported punching or hitting someone, and 4% reported
using a knife or gun on someone. Soldiers who were de-
ployed and exposed to highest combat intensity reported
more minor and severe physically aggressive actions com-
pared with those who had not previously deployed. In multi-
variate analyses, the factors most strongly associated with
minor and major aggression in the last year were lifetime his-
toryof physical altercationswith a significant other, high combat
intensity, and alcohol misuse (Table 1) (50). The authors ac-
knowledge that the sample may not have been representative
of all US Army soldiers, thus limiting the generalizability of
the prevalence findings. They further showed that, in compar-
ison with nondeployed soldiers, high combat exposure was
significantly associated with general criminal behavior and
physical altercations with a significant other (Table 1) (52).
Indeed, the strength of the associations increased with in-
creased cumulative exposure to combat.

In a national survey of a sample of 1,388 formerly serving
US military personnel drawn from a random selection of over
1 million veterans, Elbogen et al. (53) found that over a third
reported violent or aggressive behavior in the past year (using
a composite measure from the Conflict Tactics Scale and the
McArthur Community Violence Scale), although mostly in-
volving minor aggressive behavior. Eleven percent reported
oneormoreactsof severenon–combat-relatedviolence. In this
study, the authors stratified for “severe violence” (e.g., use of
a weapon, threatened with a weapon, sexual violence) and

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Table 1. Summary of Methodology and Results From Studies Published Between January 1, 2001, and February 12, 2014, in the United States and United Kingdom

First Author, Year
(Reference No.)

Study Population
Exposures

Types of Violence
and Timing

Findings
Sample Size, No. Location Data Type Population

Longitudinal studies

Elbogen,
2014 (59)a

1,388 United States Postal survey National sample
from
Department of
Veteran Affairs

Combat exposure,
violence prior to
military service,
PTSD, and alcohol
misuse

“Severe violence” or
“other physical
aggression” in past
year

9% severe violence; 26% other physical
aggression in last year. Severe
violence/aggression associated with
violence prior to military (OR = 3.95,
95% CI: 2.05, 7.62, P = 0.0001;
OR = 2.51, 95% CI: 1.44, 4.37,
P = 0.0011); combat exposure
(OR = 1.03, 95% CI: 1.01, 1.05,
P = 0.0066; OR = 1.04, 95% CI: 1.02,
1.05, P = 0.0001); and comorbid
diagnosis of PTSD and alcohol use
(OR = 4.09, 95% CI: 1.91, 8.77,
P = 0.0003; OR = 3.45, 95% CI: 1.83,
6.50, P = 0.0001).

Sullivan,
2014 (64)a

1,388 United States Postal survey National sample
from
Department of
Veteran Affairs

Combat exposure,
history of violence
prior to military
service, PTSD, and
alcohol misuse

“Severe violence” or
“other physical
aggression” toward
family or toward
stranger in past year

Family-directed acts in last year: 12.8%
other physical aggression and 3.1%
severe violence. Stranger directed
acts: 9.5% aggression and 4.8%
severe violence. High combat
associated with severe family violence
(OR = 3.96, 95% CI: 1.30, 12.02,
P = 0.0153), stranger aggression
(OR = 2.47, 95% CI: 1.39, 4.37,
P = 0.002), and severe stranger
violence (OR = 2.58, 95% CI: 1.14,
5.85, P = 0.0234).

MacManus,
2013 (60)b

13,856 United Kingdom Questionnaire survey United Kingdom
military
population

Self-reported
deployment, role on
deployment, combat
exposures,
postdeployment
mental health (PTSD,
alcohol misuse,
aggressive behavior)

Offending records from
United Kingdom
Ministry of Justice
Police National
Computer database

11% lifetime record of violent offense and
7% violent offenses postdeployment.
Preservice violent offending strongest
predictor of violent offending
(aOR = 1.79, 95% CI: 1.34, 2.39,
P < 0.0001). Deployment not
associated with violent offending.
Combat role associated with violent
offending (aHR = 1.53, 95% CI: 1.15,
2.03; P = 0.003). Increased exposure
to traumatic events during deployment
associated with risk of violent
offending (aHR = 1.65, 95% CI: 1.12,
2.40, P = 0.01; test for trend,
P = 0.032).

Killgore,
2008 (56)

1,252 Questionnaire survey US Army members
returned from
active duty

Combat experiences Risk-taking propensity
and aggressive
behaviors in the last
month

2.2% got into a fight and hit a person, and
27% reported physical aggression.
Violent combat exposure a predictor of
risk-taking propensity (r = 0.30,
F = 23.71, P < 0.001). No. of combat
exposures correlated with verbal
aggression and threats of violence.
Killing the enemy and killing of
nonhostiles were correlated with
actual physical aggression toward
others (r = 0.06, P < 0.05; r = 0.11,
P < 0.0005, respectively).

Table continues

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Table 1. Continued

First Author, Year
(Reference No.)

Study Population
Exposures

Types of Violence
and Timing

Findings
Sample Size, No. Location Data Type Population

Wright,
2012 (57)

1,397 United States Questionnaire survey US Cavalry
regiment

Combat exposure and
internalizing
symptoms
(depression and
anxiety)

Aggressive behavior in
past month

67.3% endorsed aggressive behavior.
Combat exposure had small direct
association with externalizing
behaviors at follow-up (standardized
path estimate = 0.14, P < 0.007) after
accounting for internalizing symptoms
and social environment.

Rabenhorst,
2012 (63)

4,874 couples
(6,063
individuals)

United States Military records National US
military sample

Deployment Rates of spousal abuse
according to pre- and
postdeployment
official military records

Among abusive couples, the overall
spousal abuse rate was 12.6% lower
postdeployment. In couples where
only one spouse abused and alcohol
was involved, the abuse rate was
significantly higher postdeployment. In
couples where only the husband
abused, the moderate or severe abuse
rate was 24.0% higher
postdeployment (RR = 1.24, 95% CI:
1.084, 1.444, P < 0.001), and when
alcohol was used the abuse rate was
36.8% higher postdeployment
(RR = 1.368, 95% CI: 1.055, 1.775,
P < 0.05).

Schmaling,
2011 (65)

546 United States Questionnaire survey Nonrandom
married or
cohabiting
personnel
deployed to OIF

Rank, duty status, years
in the service,
previous
deployments, and
area of the most
recent deployment

IPV and relationship
dissolution in past year

At demobilization, 13.5% of participants
reported IPV in the prior year.
Deployment was not associated with
IPV.

Cross-sectional studies

MacManus,
2012 (54)b

10,272 United Kingdom Questionnaire survey Random United
Kingdom military
population
sample

Role on deployment,
combat exposures,
postdeployment
mental health (PTSD,
symptoms of common
mental disorder,
alcohol misuse)

Aggressive behavior in
the weeks following
homecoming

12.6% were physically violent to either a
member of their family and/or
someone outside of their family.
Violence associated with combat role
(aOR = 2.0, 95% CI: 1.6, 2.5) and
increased exposure to traumatic
events (aOR for ≥4 traumatic
events = 3.7, 95% CI: 2.5, 5.5).

Tsai,
2013 (61)

30,968 United States Record based US Department of
Veteran Affairs
records

Service in OEF/OIF/
OND, combat
exposure, and records
of mental health
diagnoses

Percentage of OEF/OIF/
OND veterans
incarcerated and
incarcerated for a
violent offense. Risk of
incarceration among
OEF/OIF/OND
veterans compared
with veterans of other
eras and risk of
incarceration for a
violent offense

OEF/OIF/OND veterans less than half as
likely as other veterans to be
incarcerated and constituted only
3.9% of the incarcerated veterans;
37.5% of OEF/OIF/OND incarcerated
veterans committed violent offense.
The prevalence of violent offenders
was similar among veterans of all eras.
OEF/OIF/OND veterans were more
likely to report combat exposure and
were 3 times more likely to have
combat-related PTSD.

Booth-Kewley,
2010 (49)

1,543 United States Questionnaire survey US Marines
combat units

Combat exposure score,
PTSD symptoms, and
deployment-related
stressors

ASB scale in past year 22.9% scored high on ASB scale. The
intensity of combat exposure was
positively associated with ASB (very
high combat: aOR = 1.81, 95% CI:
1.20, 2.73, P < 0.001).

Table continues

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Table 1. Continued

First Author, Year
(Reference No.)

Study Population
Exposures

Types of Violence
and Timing

Findings
Sample Size, No. Location Data Type Population

Elbogen,
2012 (53)a

1,388 United States Postal survey National sample
from
Department of
Veteran Affairs

Combat exposure,
PTSD, and alcohol
misuse

Severe violence or other
physical aggression in
past year

33% committed ≥1 act of noncombat-
related violence/aggression, and
11% committed ≥1 act of severe
noncombat-related violence. Severe
violence associated with combat
exposure (aOR = 3.0, 95% CI: 1.85,
3.46, P < 0.001), alcohol misuse
(aOR = 2.0, 95% CI: 1.28, 3.11,
P = 0.0023), previous criminal arrests
(aOR = 1.70, 95% CI: 1.07, 2.71,
P = 0.0259), PTSD (aOR = 1.93, 95%
CI: 1.21, 3.07, P = 0.0054), and
homelessness (OR = 2.05, 95% CI:
1.0, 4.19, P = 0.0488).

Gallaway,
2012 (50)c

6,128 United States Questionnaire survey US Army combat
units

Combat exposure in
previous deployment,
PTSD, depression,
and alcohol misuse

Major and minor physical
aggression in last year

8% physical altercation with someone,
22% punching or hitting someone,
39% pushing or shoving someone, 4%
using a knife or gun on someone.
Minor aggression was associated with
lifetime history of physical altercations
with significant other (exp(β)d = 2.6,
SE, 0.2, P < 0.01) and high combat
intensity (exp(β) = 1.6, SE, 0.1,
P < 0.01). Severe physical aggression
was associated with lifetime history of
physical altercations with significant
other (exp(β) = 2.5, SE, 0.1, P < 0.01)
and high combat intensity (exp(β) =
1.5, SE, 0.1, P < 0.01).

Gallaway,
2013 (52)c

6,002 United States Questionnaire survey US Army combat
units

Combat exposure,
PTSD, depression,
alcohol misuse, and
self-reported criminal
history (conviction)
since joining military

Major and minor physical
aggression in last year

25.8% minor aggression, 21.0% major
aggression, and 8% having a physical
altercation with a significant other in
the last year. Intensity of combat
exposure was associated with severe
aggression (aOR = 2.93, 95% CI: 2.4,
3.6), minor aggression (aOR = 3.52,
95% CI: 2.9, 4.3), reporting a physical
altercation with a significant other
(OR = 1.78, 95% CI: 1.3, 1.6), and a
criminal conviction since joining the
army (OR = 2.69, 95% CI: 1.8, 4.0).

Hellmuth,
2012 (48)

653 United States Clinical assessment
questionnaire

Clinical sample
from
Department of
Veteran Affairs
clinic

Trait anger, PTSD
symptoms, and
alcohol misuse

Aggression in the last
4 months

31.8% with at least one act of physically
aggressive behavior in the past 4
months, 27.7% with less severe
physical aggression (i.e., threatening
without a weapon), and 18.9% with
more severe physical aggression (i.e.,
physical fight and threatening with a
weapon).

Sayers,
2009 (62)

199 United States Clinical assessment
questionnaire

Clinical sample
from
Department of
Veteran Affairs
clinic

Combat exposure,
PTSD, and alcohol
misuse screening

Family reintegration
problems, including
self-reported domestic
aggression in the past
year

Over 75% of married or cohabiting
veterans reported some type of family
problem in the past week; 53.7% of
veterans with current or recently
separated partners reported conflicts
involving shouting, pushing, or shoving.

Table continues

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Table 1. Continued

First Author, Year
(Reference No.)

Study Population
Exposures

Types of Violence
and Timing

Findings
Sample Size, No. Location Data Type Population

Other study types

Jakupcak,
2007 (66)

117 United States Clinical assessment
questionnaire

Clinical series
sample

Combat exposure and
PTSD

Aggression (time period
not specified)

53.2% in PTSD group and subthreshold
PTSD group endorsed at least one act
of aggression compared with 20.4% in
non-PTSD group. Combat exposure
was positively associated with trait
anger and hostility but not with
aggression. Veterans who screened
positive for PTSD reported greater
recent aggression than did veterans
who screened negative for PTSD
(exp(β) = 4.17, 95% CI: 1.6, 10.7,
P < 0.001) (after controlling for age and
problem drinking).

Thomas,
2010 (19)

13,226 United States Questionnaire survey US combat brigade
team

N/A Aggressive behavior in
the past month

Prevalence of aggression stable
between 3 months and 12 months
postdeployment: 35%–43%of soldiers
threatened someone with physical
violence or got angry enough with
someone to kick, smash, or punch
something, and 18% had gotten into a
fight with someone and hit the person.

Abbreviations: aOR, adjusted odds ratio; aHR, adjusted hazards ratio; ASB, antisocial behavior; CI, confidence interval; IPV, intimate partner violence; N/A, not applicable; OEF, Operation Enduring

Freedom; OIF, Operation Iraqi Freedom; OND, Operation New Dawn; OR, odds ratio; PTSD, post-traumatic stress syndrome; RR, rate ratio; SE, standard error.
a Elbogen, 2012 (53),Elbogen, 2014 (59), and Sullivan, 2014 (64) are based on the same study sample.
b McManus, 2012 (54) and MacManus, 2013 (60) are based on the same study sample.
c Gallaway, 2012 (50) and Gallaway, 2013 (52) are based on the same study sample.
d Exponentiation of the β coefficient, which is an odds ratio.

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“other physical aggression” (e.g., kicking, slapping, using
fists, and getting into fights) (Table 1). Self-reported combat
exposure and a previous arrest record were both independent
predictors of both “severe violence” and “other physical ag-
gression” on multivariate analyses (53).
Our group at King’s College London used nonanonymous

questionnaire data from a randomly selected sample of
10,272 United Kingdom military personnel in service at the
time of the Iraq War in 2003 to explore the prevalence of and
risk factors for violence following return from deployment,
accounting for preenlistment antisocial behavior (Table 1)
(54); 12.6% of Regulars reported having physically assaulted
someone “in the weeks following deployment” (not a very
precise outcome time period). Preenlistment antisocial be-
havior was the strongest predictor of this violence. After con-
trolling for sociodemographic and military factors as well as
preenlistment antisocial behavior, we found that combat role
was still strongly associated with postdeployment violence.
Consistent with other studies, our study found that the
strength of the association with self-reported violence was
shown to increase with the cumulative increase in number
of exposures to traumatic events in combat.
In spite of the variation in outcome measurement, the ma-

jority of cross-sectional studies found a small-to-moderate
association (odds ratio = 1.5–3.5) (55) between combat expo-
sure, or specific combat experiences, and postdeployment
physical aggression and violence, with several studies finding
that the risk of violence increased with increased intensity
and frequency of exposure to combat traumas (Table 1).

Self-reported aggression and violence: longitudinal studies.
The temporal sequence of outcomes following the indepen-
dent variables of longitudinal studies is a major advantage
for causal inference. Killgore et al. (56) explored the link be-
tween different combat experiences reported immediately on
return from deployment and risk-taking behaviors and aggres-
sive behaviors reported 3 months later in a sample of 1,252 US
soldiers returned from Operation Iraqi Freedom (42% of the
original nonrandom sample) (Table 1). They found that
2.2% reported getting into a fight and hitting the person in
the last month. The most consistent predictor of risk-taking
propensity was “violent combat exposure,” which remained
significant after controlling for demographic confounders,
but it did not predict actual physical violence, probably be-
cause of low statistical power. A number of combat exposures
were significantly correlated with verbal aggression and threats
of violence, but killing the enemy and killing of nonhostiles
were the only combat factors significantly correlated with ac-
tual physical aggression toward others in the preceding month.
Wright et al. (57) explored the link between combat expo-

sures, externalizing behaviors (e.g., alcohol misuse, aggres-
sive behavior, and risk-taking behavior), and internalizing
symptoms in a survey of 1,397 (42%) soldiers from a USmil-
itary unit 4 and 9months postdeployment (only 589 followed
up at 9 months) (Table 1). Their validated 4-item aggression
scale (58) included an item on getting into a fight and hitting
someone, as well as threatening violence. Notably, the sam-
ple reported experiencing high levels of combat exposure
during their last deployment; 67% reported aggressive behavior
in the past month, but this included verbal and physical threats
of aggression and property aggression so it is not comparable

with estimates of physical aggression alone. Combat exposure
was associated with externalizing behaviors at both 4 and 9
months in the cross-sectional and longitudinal analyses, even
after controlling for internalizing and social environment fac-
tors (57). Unfortunately they did not report on any separate re-
lationship or path from combat exposure to individual
externalizing behaviors, such as aggressive behavior.
Elbogen et al. (59) followed up their national sample of

1,388 formerly serving Iraq and Afghanistan veterans after
1 year (with a good retention rate of 79%). Overall, 9% en-
dorsed engaging in severe violence (e.g., use of a weapon,
threatened with a weapon, sexual violence) and 26% in
other physical aggression (e.g., kicking, slapping, using
fists, and getting into fights) in the previous year. This is
one of the only studies, along with those by MacManus
et al. (54, 60), to adjust for history of violence before military
service, an important preenlistment factor. When this covar-
iate and other covariates were adjusted for, combat exposure
was still associated with severe violence and other aggressive
behavior (Table 1) (59). Overall the longitudinal studies gen-
erally support the findings of the cross-sectional studies. The
association between combat and aggression or violence
ranges from small to moderate (odds ratio = 1.5–3.5) (55)
even after adjustment for premilitary violence.

Offending records and incarceration studies. Tsai et al.
(61), reported on a national study of 30,968 incarcerated for-
merly serving personnel, including 1,201 Iraq and Afghani-
stan veterans as well as those from other conflict eras
(Table 1). Once again, the most common category of offense
was violent offenses, and the proportion of incarcerated Iraq
and Afghanistan veterans who were incarcerated for violent
offenses was similar to the proportion of incarcerated veter-
ans of other conflict eras incarcerated for a violent offense
(37.5 vs. 35%). Iraq and Afghanistan veterans were more
likely to report combat exposure and to suffer from combat-
related PTSD than were other veterans. However, despite
being a study of incarcerated veterans, it still relied on self-
reported criminal offenses and nonstandardized measures
of diagnoses and did not take account of the time since de-
ployment. Hence, the finding that the most recent veterans
(i.e., Operation Enduring Freedom/Operation Iraqi Free-
dom/Operation New Dawn) were less likely to be incarcer-
ated may simply reflect differences in the time at risk rather
than any true differences.
The King’s College London group were able to link com-

prehensive data from a longitudinal study of a nationally
representative sample of almost 14,000 United Kingdommil-
itary personnel with national offending records (Table 1)
(60). Overall, the results were congruent with the previous
work based on self-report of violence. Deployment itself
was not found to be a risk for violent offending, but being
deployed in a combat role and an increased burden of trauma-
tic events on deployment significantly predicted subsequent
violent offending. Although a history of violent offending
prior to joining the military was the strongest risk factor for
postdeployment violent offending, after adjustment for this
factor and other factors, combat role and deployment-related
traumatic events were still predictors of subsequent violent
offending. While studies that use conviction records fail to
capture the offenses that do not come to the attention of the

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police, they provide an objective assessment of the most se-
rious offences, that is, those that attract a conviction.

Domestic violence

Fewer studies were found that focused on domestic or family
violence among Iraq or Afghanistan veterans. In a cross-
sectional survey of a small clinical population (n = 199), Sayers
et al. (62) investigated family problems among recently
returned military veterans who had served in Iraq or Afghan-
istan and who presented for a medical evaluation at the Phil-
adelphia Veterans Affairs Medical Center (Table 1). Among
veterans with current or recently separated partners, 54% re-
ported conflicts involving shouting, pushing, or shoving in
the past year. However, as the authors acknowledge, this was
a small sample that was not representative of the US military.

Rabenhorst et al. (63) conducted the first population-based
study of 4,874 married US Air Force personnel couples that
compared spousal abuse rates (as recorded in military re-
cords) before and after combat-related deployments during
Operation Enduring Freedom/Operation Iraqi Freedom
(Table 1). They reported rates of incidents among coupleswho
were engaging in partner abuse as opposed to the prevalence
of perpetrators pre- and postdeployment. Among all abusive
couples, the overall spousal abuse rate was 12.6% lower post-
deployment. However, among specific couples in which only
the husband abused and the abusewas moderate to severe, the
rate increased. The rate increased evenmore if alcohol misuse
was reported. A strength of this study is the use of objective
record–based outcomes but, of course, as stated previously,
studies that look only at recorded incidents are thought to un-
derestimate the rates of violence, especially of domestic vio-
lence. This study is also limited to the Air Force, which,
probably because of differences in selection and education,
has lower rates of violent behavior than the other services.

In their 1-year follow-up study of their national sample of
1,090 US military personnel, Sullivan and Elbogen (64)
compared rates of stranger versus family aggression and vio-
lence (the terms “severe violence” and “other physical ag-
gression” merely distinguish between levels of severity of
physical aggression) (Table 1); 13% reported any physical
aggression or violence toward a family member during the
year of study. This is a self-reported measure and may be an
underestimation, but it is of interest that family-directed ag-
gression or violence was found to be commoner than stranger-
directed aggression or violence (9%). A history of arrest was
positively associated with both stranger physical aggression
and severe violence but not family physical aggression or se-
vere violence. High combat exposure strongly predicted stran-
ger aggression and severe violence, and it predicted severe
family violence but not family aggression.

Schmaling et al. (65) conducted a longitudinal examina-
tion of predictors of intimate partner violence among 546 re-
servist military personnel using data from before and after
mobilization for Operation Iraqi Freedom (Table 1). Follow-
ing demobilization, 13.5% reported engaging in intimate
partner violence in the previous year. However, this may be
more a reflection of intimate partner violence during deploy-
ment rather than postdeployment. They also found that
deployment was associated with less stress and more relation-

ship satisfaction, but it is important to note that most of the
sample were not on active duty and had not served before,
so the results cannot be extrapolated to troops deployed on
active duty or exposed to combat.

Overall, only 4 studies were found that examined domestic-
related violence or explored the relationship between deploy-
ment and combat and domestic violence among Iraq and
Afghanistan veterans. Although their methodological rigor
varies, overall they suggest that aggression and violence within
the familymaybeasprevalent asgeneral aggressionandviolence
and that, among regular troops, these behaviors may increase
after deployment (although this was not shown among reserv-
ists who are not deployed on active duty (65)), and this may be
related to the intensity of combat exposure. More research is
required before any meaningful conclusions can be drawn.

Impact of premilitary violence

A number of the studies found that previous aggression and
violence is more strongly associated with self-reported postde-
ployment violence than any deployment-related risk factor, in-
cluding having served in a combat role (50, 54, 59). We, at
King’s College London, took this further by looking longi-
tudinally at postdeployment violent offending using official
offending records and were therefore able to control for pre-
military violent offending (objective records). We found that
it was the strongest risk factor for postdeployment violent of-
fending (60). This was adjusted for in our multivariate analyses
exploring the link between deployment and combat and post-
deployment violent offending.

Meta-analyses

Prevalence studies. Of the 17 papers reviewed, 10 were
included in meta-analyses of prevalence of aggressive or vi-
olent behavior postdeployment. Papers were excluded for a
range of reasons: 5 papers contained data from overlapping
samples (50, 52, 53, 59, 64) so only data from the 2 original
studies were included (50, 53); 3 studies concerned intimate
partner violence, spousal abuse, or domestic violence, and
heterogeneous outcomes precluded a separate meta-analysis
of the prevalence of intimate partner violence postdeploy-
ment (62, 63, 65); 1 study explored official offending records
(60); and 1 examined rates of incarceration for violence (61).
The outcomes of 2 further studies were not suitable for com-
bination in a meta-analysis.

We examined studies that included a measure of “all ag-
gressive behavior” postdeployment first (48, 49, 53, 56, 57)
and then examined studies that specifically examined behav-
ior that involved physically hitting someone in the postde-
ployment period (19, 48, 50, 54, 56). Figure 2 shows the
forest plot of the weighted estimated mean prevalence of
“all aggressive behavior.” The pooled estimate of prevalence
was 36% (95% confidence interval (CI): 25, 48); this estimate
had significant heterogeneity (I2 = 99.1%). The influence of
one study (57) that included “verbal aggression” in their out-
come measure on the pooled prevalence rate was explored by
repeating the meta-analysis omitting this study. The pooled
estimate reduced to 29% (95% CI: 25, 36), but the hetero-
geneity remained high (I2 = 95.6%). The subgroup analyses

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illustrated in Figure 3 show forest plots of the weighted esti-
mated mean prevalence of “hitting someone” postdeploy-
ment in the last month or a longer period and show pooled
estimates of 10% (95% CI: 1, 20) for the past month and
14% (95% CI: 6, 22) for the past year. Heterogeneity was
lower among the 2 studies that explored the outcome in a lon-
ger prevalence period but still remained moderately high.

Association between combat and aggressive or violent
behavior. Of the 10 papers that reported results of their ex-
aminations of the association between combat exposure and
general aggression and violent behavior (49, 50, 52–54, 56,
57, 59, 60, 64), only 3 could be included in the meta-analysis.
Seven papers contained overlapping data from 3 original
study samples (50, 52–54, 59, 60, 64), and 3 studies did

Overall (I2
= 99.1%, P = 0.000)

Author, Year (Reference No.)

Booth-Kewley, 2010 (49)

Hellmuth, 2012 (48)

Wright, 2012 (57)

Elbogen, 2012 (53)

Killgore, 2008 (56)

0.36 (0.25, 0.48)

ES (95% CI)

0.23 (0.21, 0.25)

0.32 (0.28, 0.35)

0.67 (0.63, 0.71)

0.33 (0.31, 0.35)

0.27 (0.25, 0.29)

100.00

20.11

19.87

19.82

20.06

20.14

% Weight

0 0.2 0.4 0.6 0.8

Proportion

Figure 2. Forest plot of studies measuring “all aggression.” CI, confidence interval; ES, estimate [of prevalence].

Gallaway, 2012 (50)

Thomas, 2010 (19)

In Last 30 Days

Longer than 30 Days

Hellmuth, 2012 (48)

Subtotal (I2
= 99.8%, P = 0.000)

Subtotal (I2
= 73.8%, P = 0.051)

Overall (I2
= 99.7%, P = 0.000)

Killgore, 2008 (56)

MacManus, 2012 (54)

Author, Year (Reference No.)

0.22 (0.21, 0.23)

0.16 (0.16, 0.17)

0.21 (0.18, 0.24)

0.19 (0.16, 0.22)

0.10 (0.01, 0.20)

0.02 (0.02, 0.03)

0.13 (0.12, 0.14)

20.08

20.10

39.68

19.60

60.32

20.12

20.09

0.14 (0.06, 0.22)

ES (95% CI)

100.00

% Weight

0 0.2 0.4
Proportion

Figure 3. Forest plot of studies measuring “hitting/assaulting another person.” CI, confidence interval; ES, estimate [of prevalence].

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not report their findings in a manner that allowed combina-
tion with other studies (52, 56, 57). Figure 4 shows the forest
plot of the estimated weighted odds ratios for the association
between combat exposure and aggressive or violent antiso-
cial behavior postdeployment with a pooled estimate across
the 3 studies of 3.24 (95% CI: 2.75, 3.82); the level of hetero-
geneity was low (I2 = 0.0%, P = 0.394).

Studies of mediating factors

Several studies included measurement of postdeployment
psychopathology and explored the role this may have in the link
between deployment and combat and postdeployment violence.
The studies were heavily focused on PTSD as the main psycho-
pathology of interest, and some also explored alcohol misuse.

A study of a consecutive sample of 117 treatment-seeking
Iraq and Afghanistan combat veterans presenting to a Depart-
ment of Veterans Affairs center found that a significantly
higher proportion of veterans with PTSD (53.2%) and sub-
threshold PTSD (52.4%) reported at least one act of violence
in the past 4 months compared with a group without PTSD
(20.3%) (Table 1) (66). They also found that those who
screened positive for PTSD and subthreshold PTSD also re-
ported greater aggressive behavior than those without PTSD.
Although such a study is an initial indicator of a possible link
between PTSD and violence among veterans of these con-
flicts, more robust methodology is needed to explore associ-
ations and mediation. Booth-Kewley et al. (49) found in their
cross-sectional analyses that combat-exposed Marines with
PTSDwere over 6 times more likely to engage in antisocial be-
havior than those who did not have PTSD, thus suggesting an
association between PTSD and antisocial behavior amongMa-
rines who had combat experience. In our cross-sectional popu-
lation study of the United Kingdom Armed Forces, we found
that mental health problems such as PTSD, alcohol misuse, and
symptoms of common mental disorders were strongly associ-
ated with self-reported postdeployment violence (54, 60).

Further, by linking our data with national offending registers to
provide the timings of offending behavior, we show that post-
deployment violent offending was predicted by previously re-
ported postdeployment mental health and behavior problems
(PTSD and alcohol problems and to lesser extent “symptoms
of common mental disorder”) and indeed that these problems
mediated some of the link between combat and traumatic expo-
sures and violent offending (60). In the longitudinal study by
Elbogen et al. (59) described above, they found that veterans
with both PTSD and alcohol misuse had a substantially higher
rate of subsequent severe violence (35.9%) comparedwith veter-
ans with alcohol misuse without PTSD (10.6%), PTSD without
alcohol misuse (10.0%), or neither PTSD nor alcohol misuse
(5.3%). Upon multiple regression, veterans with PTSD without
alcohol misusewere not at significantly higher risk of severe vio-
lence than were veterans with neither PTSD nor alcohol misuse.

Hellmuth et al. (48) modeled how PTSD symptom clusters,
alcohol misuse, and anger related to aggression using pathway
analysis of cross-sectional data from their clinical sample of
359 US Iraq and Afghanistan War veterans (Table 1). The
PTSD-reexperiencing cluster and alcohol misuse were found
to relate directly to aggression, whereas the PTSD-numbing
and -hyperarousal clusters were indirectly related to aggression
through trait anger.We found that, of the PTSD symptom clus-
ters, the hyperarousal cluster wasmost strongly associated with
subsequent violent offending (60). In their longitudinal study
described above, Sullivan and Elbogen (64) found that PTSD
anger symptoms predicted family aggression and violence but
not stranger aggression and violence and that PTSD flashbacks
predicted stranger aggression and severe violence but not fam-
ily aggression and violence.

DISCUSSION

This review has appraised 17 papers that have investigated
postdeployment violence, both general violence and violence
against family, spouses, and partners, among veterans of the

Overall (I2
= 0.0%, P = 0.394)

Author, Year (Reference No.)

MacManus, 2012 (54)

Booth-Kewley, 2010 (49)

Elbogen, 2014 (59)

0.0 2.0 3.0 4.0

Odds Ratio

1.0 8.0

ES (95% CI) % Weight

2.61 (0.70, 9.71) 1.58

2.72 (1.99, 3.72) 27.65

3.49 (2.87, 4.25) 70.78

3.24 (2.75, 3.82) 100.00

Figure 4. Forest plot of studies that examined the association between combat and aggression. (Data for the study by Elbogen et al. (59) use data
pertaining to “other aggression.”) CI, confidence interval; ES, estimate [of odds ratio].

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Iraq and Afghanistan conflicts. A number of the studies also
explored the role of postdeployment psychopathology in
the mediation of the link among deployment, combat, and
violence.

Prevalence of postdeployment aggression and

violence

The range of definitions and measures of aggression and
violence continues to make interstudy comparisons difficult
as studies used a different measure of aggression and vio-
lence or used the same measures but with different cutoffs
or over different time periods. If we consider studies with
the most similar outcome measure of physical acts of vio-
lence postdeployment, the pooled estimates of 10% in the
last month and 20% in the longer time period should be ac-
cepted with caution given the high level of heterogeneity
among the studies. This high heterogeneity could be in part
explained by levels of operational tempo and combat expo-
sure, enlistment status (still serving or nonserving personnel),
and other specific characteristics of the study. The range of
estimates in the United Kingdom compared with the United
States was as follows: In the United Kingdom, 13% of a rep-
resentative sample of serving and formerly serving deployed
military personnel self reported getting into afight and hitting
someone in the weeks following deployment (54); 18% of a
fairly comparable representative sample of deployed US
troops self reported getting into a fight and hitting someone
in the past month (19); a comparatively lower proportion of
2.2% of a nonrandom sample of returned Iraq veterans re-
ported hitting someone in the last month in another study
(56), and an apparently higher proportion, 22%, of a sample
of still serving US combat personnel who reported high
levels of combat exposure reported punching or hitting
someone, but the time period of the last 12 months was com-
paratively longer (50). Studies that reported overall ag-
gression found higher prevalence rates (pooled estimate of
29%–36% depending on whether verbal aggression was
measured).
The self-report nature of most of the outcome measures re-

mains a limitation of research in this area. As far as we know,
we are the only group to date that has accessed objective mea-
sures of postdeployment violence (i.e., convictions) and, as
expected, found that a lower percentage, 8% (which is also
over a longer period of time), of our large representative sam-
ple of United Kingdom military personnel had a record of
a violent offense postdeployment (60). The lack of studies
that have explored aggression and violence among military
personnel limits the possible exploration of differences be-
tween those still serving compared with formerly serving
personnel.
We found only one study that estimated the prevalence of

postdeployment intimate partner violence perpetration
among a nonclinical sample of Iraq and Afghanistan veteran
reservists (65). Rabenhorst et al. (63) looked at rates of inci-
dents among couples who were engaging in partner abuse as
opposed to prevalence of perpetrators pre- and postdeploy-
ment. Sullivan and Elbogen (64) found that 13% of their na-
tional sample of nonactive Iraq and Afghanistan veterans
reported physical aggression and violence toward a family

member, which is an important differentiation from stranger
violence although it does not specify partner violence.
In summary, estimates of the prevalence of postdeploy-

ment violence among Iraq and Afghanistan veterans depend
on the sample under study and the definition and measure of
aggression and violence used. With one exception (56), the
studies in this review highlight that this behavior is prevalent
among serving and formerly serving personnel (estimates of
10% for physical assault and 29% for all types of physical
aggression in the last month) and worthy of further explora-
tion. Further research into the prevalence of postdeployment
domestic violence is required, especially into partner- and
family-directed violence.

Impact of deployment and combat on risk of

postdeployment aggression and violence

Most of the research into violence among combat veterans
has been carried out in the United States, much of which has
utilized data from past conflicts, such as the VietnamWar and
the 1990–1991 Gulf War. The results have been mixed. A
number of these studies found associations between combat
exposure (rather than deployment) and physical aggression
and incarceration postdeployment (24–28). However, other
studies did not find that combat exposure itself but rather cer-
tain combat exposure, such as participating in war-zone vio-
lence, predicted violence postdeployment (31). Others found
premilitary characteristics to be the strongest risk factor for
postdeployment violence (32, 33). Postdeployment intimate
partner violence is a form of violence that has received much
research attention in the United States. A number of pre–
Operation Enduring Freedom/Operation Iraqi Freedom studies
found an association between combat exposure and intimate
partner violence perpetration (29, 30, 67). In contrast, a num-
ber of studies found no significant difference in the perpetra-
tion of domestic violence between veterans with combat
experience and those without, although these studies did
not examine specific combat-related variables (68).
In this review of studies of Iraq and Afghanistan, in spite of

the variation in outcome measurement and study design, the
majority of studies supported a small-to-moderate (55) as-
sociation between combat exposure and postdeployment
physical aggression and violence (42, 49, 50, 52–54, 56, 57,
60, 69) with several studies finding that the risk of violence
increased with increased intensity and frequency of exposure
to combat “traumas” (50, 52, 54, 60). Our limited meta-
analysis of a subset of studies from both the United States
and the United Kingdom estimated a pooled unadjusted odds
ratio of 3.24 (95% CI: 2.75, 3.82). Despite the limitations of
cross-sectional studies, their results are consistent with those
studies which have used a longitudinal design. The only
population-based longitudinal study that utilized an objective
measure of both premilitary violent offending and postde-
ployment violent offending confirmed these findings (60).
The major limitation of most of the research to date among

Iraq and Afghanistan veterans has been the neglect of pre-
military risk of violence. Background violence risk factors are
important to consider in the etiology of postdeployment vio-
lence when attempting to tease out the relative impact of de-
ployment and combat. Research from the general population

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has shown that childhood antisocial behavior impacts on later
antisocial behavior and criminality (70). Premilitary antisocial
behavior may reflect a predisposition for such behavior,
which may continue into adulthood irrespective of the impact
of military service. Our group at King’s College London
found that the impact of preenlistment antisocial behavior
on negative military behavioral outcomes in personnel de-
ployed to Iraq was strongly independently associated with se-
vere alcohol misuse, outbursts of anger or irritability, fighting
or assaultative behavior, and risk-taking behavior (71). A
number of studies of veterans from the Vietnam era found
that prewar antisocial behavior was a stronger predictor of
veteran violence than combat exposure (32, 33, 72). Similar
to the Vietnam-era literature, the studies in this review of the
Iraq and Afghanistan eras found that previous antisocial be-
havior or aggression was more strongly associated with post-
deploymentviolence thancombatexposure.However, combat
exposure was still significantly associated on multivariable
analyses (50, 54, 60). This review shows clearly that the as-
sociation between combat and violence cannot be explained
away solely by selection and ipso facto that improved recruit
screening will not solve the problem. Whether or not better
training or better postdeployment support might mitigate
the link is an empirical question that we have not yet begun
to address. However, the seductions of screening for vulner-
ability mean that it is something that is proposed from time to
time for various reasons, even if there is still a lack of any ro-
bustevidencebase tosupport it (73).One reason fornot screen-
ing out those at risk of perpetrating violence is that it is well
recognized by the military and the public alike that a propor-
tion of military recruits come from difficult backgrounds and
that enlisting in the military may be the changing point in the
lives of many who go on to acquire education, training, skills,
discipline, and self-esteem that they might never otherwise
have had the opportunity to achieve (74). This review, how-
ever, clearly demonstrates that, for some, the military may
provide an environment for continued and increasing violent
behavior. These results highlight that ongoing violent behav-
ior and increased violence postdeployment may be a concern
among military personnel, especially among those with a his-
tory of offending prior to enlistment.

The role of psychopathology in the link between

deployment to Iraq and Afghanistan and postdeployment

violence

Most studies from the pre-Iraq and Afghanistan eras pro-
posed that PTSDwas an important mediator in the association
between combat (trauma) and violent behavior (34–37). PTSD
was frequently shown to be significantly related to both combat
and violent and aggressive acts among veterans of previous
conflict eras (27, 33, 40, 75–79). A body of research also estab-
lished that a relationship exists between PTSD and intimate
partner violence perpetration among US veterans (36, 80), and
some have found the association between certain deployment
experiences and intimate partner violence to be largely ac-
counted for by PTSD symptoms (29).

Similar to pre-Iraq and Afghanistan studies, many studies
of Iraq andAfghanistan veterans demonstrated a link between
PTSD and postdeployment violence (42, 54, 59, 66), and

some have provided evidence that PTSD can play amediating
role between combat exposure and violence (48, 60). Studies
of pre-Iraq and Afghanistan era veterans found different as-
pects of the symptomatology to be specifically related to
postdeployment violence, such as hyperarousal (40, 81),
avoidance and numbing symptoms (40), or comorbid dys-
phoria (81). Studies in this review also suggest that, among
Iraq and Afghanistan veterans, the clusters and indeed indi-
vidual symptoms of PTSD relate differently to behavior
with varying evidence for the specific role of hyperarousal
(42, 60), flashbacks (64), and PTSD-related anger and irrita-
bility (64) in postdeployment violence. To add further com-
plexity, Miller et al. (82, 83) reported that, among Vietnam
combat veterans, those who internalized combat-related
PTSD had high prevalence rates of panic and depression
and were more likely to experience their distress internally
through mood and thoughts. Those who externalized were
more likely to express distress outwardly through behaviors
and had high rates of antisocial personality traits, alcohol-
related behaviors, and histories of delinquency. Rielage
et al. (84) showed that this personality model of PTSD co-
morbidities can also be applied in the Iraq and Afghanistan
veteran populations. Thus, the earlier studies showing a
link between PTSD and postdeployment violence may not
account for personality traits.

Although PTSD is perhaps the most researched diagnosis
when considering violence in combat veterans, there is liter-
ature suggesting that other psychopathologies can be linked
with violence. Alcohol misuse has been shown to be strongly
associated with aggressive behavior among combat veterans
(39, 40). PTSD with comorbid alcohol dependence has also
been shown to lead to greater violence than PTSD alone, hy-
pothetically because of the effect on hyperarousal symptoms
(39). Among studies of Vietnam veterans, direct relationships
were found between alcohol misuse and PTSD symptoms
and the frequency of intimate partner violence perpetration
(85, 86). As this review shows, evidence is also emerging
from Iraq and Afghanistan veterans to suggest the modifying
effect of alcohol misuse on comorbid conditions such as
PTSD to increase risk of postdeployment violence (48, 59).
Indeed, the most recent study by Elbogen et al. (59) has sug-
gested that, in the absence of alcohol misuse, PTSD is not
associated with severe violence postdeployment but is asso-
ciated with lesser physical aggression. These findings suggest
that adjunct treatments aimed at stabilizing anger and alcohol
misuse may help clinicians to ameliorate the maladaptive pat-
terns that are often observed in veterans.

Findings from the United States suggest high rates of post-
deployment PTSD with estimates of 10%–20% of returning
US servicemen and women experiencing symptoms (87–89).
With PTSD rates shown to be lower in the United Kingdom,
the actual impact of this risk factor on violence at a population
level may be less pertinent than among US military cohorts
(90). This does not, however, affect the importance of PTSD
as a risk factor for violence at an individual level. The con-
verse may be true for alcohol misuse, which is a greater prob-
lem among the armed forces of the United Kingdom than
among those in the United States (22) and was observed to
increase among United Kingdom combat troops following
return from deployment to Iraq or Afghanistan (16).

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Implications

This growing body of literature emerging on veterans of
the Iraq and Afghanistan conflicts provides evidence that
postdeployment violence is a problem for a subgroup of vet-
erans and that exposure to combat is one among many risk
factors for violence in this population, which may be partly
mediated by postdeployment mental health problems such as
PTSD and alcohol misuse. As both the United States and the
United Kingdom face the long-term consequences of 10
years of combat in Iraq and Afghanistan, this work provides
information for developing a strategy to tackle issues related
to risk of violence in military personnel.
However, the literature so far does not include an examina-

tion of the effectiveness of postdeployment violence screen-
ing and, therefore, despite pressure from the media in the
wake of incidents like the Fort Hood shootings (91), imple-
mentation of any screening program should be based on the
use of valid tools of assessment, as well as demonstrable
effectiveness in the management of those identified by the
program, preferably in a randomized controlled trial. Themil-
itary is composed of a range of individuals, some roles require
aggressive traits, and personnel are trained to respond to cer-
tain situations with targeted aggression. Interventions for
military personnel on return from deployment to help these in-
dividuals adapt their responses to community and family envi-
ronments may be more acceptable and potentially valuable.
This evidence can be used to begin trial interventions targeted
at the factors showing signs of being on the causal pathway.

Future research

This review has highlighted the lack of standardized prac-
tices in this area of research. We therefore recommend that
future research give more consideration to the standardization
of data collection instruments and that efforts are made to ob-
tain objective information where possible through accessing
criminal records. Research to date has been heavily weighted
toward general violence. We suggest that this needs to be
more focused and, in particular, that more work is needed
on the prevalence of and risk factors for violence against
the family by military personnel. Perhaps this will in time
also help inform prevention and management strategies.
We also have noted the focus on the role of PTSD in postde-
ployment violence, and we suggest that in the future more at-
tention perhaps needs to be given to other mental disorders
and most specifically to substance misuse.

ACKNOWLEDGMENTS

Author affiliations: King’s Centre for Military Health Re-
search, King’s College London, Weston Education Centre,
London, United Kingdom (Deirdre MacManus, Roberto
Rona, Nicola Fear, Simon Wessely); Department of Forensic
and Neurodevelopmental Science, Institute of Psychiatry,
London, United Kingdom (Deirdre MacManus, Greta
Somaini); Academic Centre for Defence Mental Health,
Weston Education Centre, London, United Kingdom (Nicola

Fear, SimonWessely); andSchool of Psychology,Universityof
West London, London, United Kingdom (Hannah Dickson).
N. F. and S. W. are employed by the Academic Centre for

Defence Mental Health, based at King’s College London,
which receives funding from the Ministry of Defence of the
United Kingdom. S. W. is also honorary civilian consultant
advisor in psychiatry to the British Army and a trustee of
Combat Stress, a United Kingdom charity that provides ser-
vice and support for veterans with mental health problems.
Financial support was also received from the Department
of Health via the National Institute for Health Research
(NIHR) Comprehensive Biomedical Research Centre Award
to Guy’s & St Thomas’ National Health Service Foundation
Trust in partnership with King’s College London and King’s
College Hospital National Health Service Foundation Trust.
Conflict of interest: none declared.

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