Leader similarity and international conflict
| Published date | 01 January 2025 |
| DOI | http://doi.org/10.1177/00223433231186446 |
| Author | Matthew DiLorenzo,Bryan Rooney |
| Date | 01 January 2025 |
https://doi.org/10.1177/00223433231186446
Journal of Peace Research
2025, Vol. 62(1) 102 –118
© The Author(s) 2023
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DOI: 10.1177/00223433231186446
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1225162JPR0010.1177/00223433231186446Journal of Peace ResearchDiLorenzo & Rooney
research-article2023
Regular Article
Leader similarity and international conflict
Matthew DiLorenzo
Department of Political Science & Geography, Old Dominion University
Bryan Rooney
RAND Corporation
Abstract
Scholars increasingly emphasize personal biographical characteristics of leaders in explaining patterns of foreign
policy behavior. This article extends insights from this agenda to study how (dis)similarities in the background
characteristics of leaders at the dyadic level shape international conflict outcomes. Trust and uncertainty are central to
explaining conflict via their connections to commitment- and information-related causes of war. Psychological
research provides evidence that perceived similarities between individuals and groups can foment trust and cooper-
ation. We hypothesize that leaders who share more similar backgrounds and life experiences form stronger social
bonds and are more trusting of one another. As such, leaders who have more in common with one another should be
able to better manage diplomatic disputes and avoid conflict. We test this hypothesis using a new measure of dyadic-
leader-level similarity created with the Leader Experience and Attribute Descriptions (LEAD) dataset and data on
international conflict onset in politically relevant dyads throughout the period 1946–2004. We find that pairs of
leaders with more similar backgrounds are significantly less likely to experience militarized interstate disputes at all
levels of hostility even after accounting for a variety of observable and unobservable determinants of conflict. The
findings contribute to our understanding of the determinants of international conflict and help advance research on
linkages between psychological and rationalist approaches to studying conflict.
Keywords
leaders, militarized interstate disputes, trust
Introduction
Recent international relations research emphasizes how
the personal biographical characteristics of leaders and
their interpersonal interactions with one another shape
foreign policy behavior and international outcomes
(Byman & Pollack, 2001; Saunders, 2011; Horowitz
& Stam, 2014; Ellis, Horowitz & Stam, 2015; Holmes
& Yarhi-Milo, 2017; Holmes, 2018; Yarhi-Milo, 2018;
Holmes & Wheeler, 2020). For example, leaders who
have served in the military but lack combat experience
are more likely to initiate militarized interstate disputes
(Horowitz & Stam, 2014: 529). This agenda has pro-
duced insights into how life experiences, personality
traits and interpersonal relationships between leaders can
shape international outcomes independently of interna-
tional and domestic political contexts.
In this article, we build on this literature by arguing
that similarity in leaders’ personal background traits at
the dyadic level can help promote positive social bonds
that build trust and rapport in ways that matter for
conflict decisions. Research in psychology suggests that
perceived similarity can promote trust and cooperation
between individuals and groups (Lui, Ngo & Hon,
2006; Fischer, 2009; Clerke & Heerey, 2021). We con-
nect this psychological argument to rationalist theories of
conflict. The incentive to misrepresent private informa-
tion and commitment problems are central explanations
for bargaining failure in international relations scholar-
ship (Fearon, 1995; Powell, 1999). We argue that when
Corresponding author:
mdiloren@odu.edu
DiLorenzo & Rooney 103
leaders share more in common in terms of their personal
backgrounds and histories, they should be able to more
credibly communicate in ways that build trust and
reduce problems associated with information asymme-
tries and commitment problems. As such, leaders who
are more similar to one another should bring their coun-
tries into conflict with each other less frequently.
We test our argument with leader-dyadic-year data
over the period 1946–2004. Using 58 leader-specific
background traits and life experiences recorded in the
Leader Experience and Attribute Descriptions (LEAD)
dataset (Ellis, Horowitz & Stam, 2015), we generate a
leader-dyadic measure of the similarity of leaders in polit-
ically relevant dyads. We include this measure in a set of
statistical models of international conflict onset at the
dyad-year level. We find that leader similarity is consis-
tently and significantly associated with a reduction in the
likelihood of a militarized interstate dispute (MID) within
dyads even when accounting for various established deter-
minants of conflict. We find that the same holdsfor MIDs
that reach high levels of hostility or those that involve
fatalities, as well as interstate wars. This pattern is further
robust to various approaches to explicitly modeling dyads’
propensities for experiencing conflict, including
propensity-weighted and selection models.
This article makes three key contributions. First, it
expands our knowledge of the determinants of interna-
tional conflict at the dyadic level. The similarity of lead-
ers is consistently a statistically significant predictor of
MID onset. Further, since it is based mostly on the
background experiences of leaders before they take
office, it is plausibly exogenous to conflict in ways that
avoid critiques often leveled against other common
determinants of MIDs. Second, we provide a new mea-
sure of leader similarity for all leaders who held power at
the same time during the temporal domain of the data
provided in the LEAD dataset. We use the measure to
study the effects of leader similarity on conflict onset,
though the conceptual and empirical frameworks we
develop could be applied to many other domains of
international relations. For instance, information and
commitment problems figure prominently into many
non-conflict-related areas such as international trade and
environmental cooperation. It is plausible that leader
similarity plays a role in explaining cooperation out-
comes in those and other domains. Finally, our research
is relevant for scholars interested in predicting and study-
ing the effects of social bonding on interstate relations
(e.g. Holmes & Wheeler, 2020). Others have developed
theories of how the conditions and setting of face-to-face
interactions may promote social bonding (Holmes &
Wheeler, 2020). This article builds on those ideas by
considering how the background experiences and attri-
butes of leaders that they bring to their interactions with
their peers can shape interpersonal relationships and
trust. Indeed, a key contribution of this article is in
extending findings from psychology which suggest that
sharing background characteristics can serve as the basis
for trust and cooperation to the study of leaders and
international outcomes.
The article proceeds as follows. In the next section we
briefly review existing literature on leader-level explana-
tions for international conflict, emphasizing work on the
psychology of decisionmaking. In the third section we
develop our argument about how the presence of shared
traits and life experiences should help leaders build trust
and establish interpersonal connections that are relevant
for international bargaining outcomes. The fourth sec-
tion describes our research design, including issues
involved in generating a measure of leader similarity that
takes into account all of the observed leader traits
included in the LEAD dataset. The fifth section presents
the results of our statistical analysis and discusses some of
supplementary analyses and robustness checks. The sixth
section concludes with a discussion of the implications of
the findings.
Trust, bonding and shared life experiences
Information and commitment problems are both ende-
mic in international relations (IR) and central explana-
tions for bargaining failure in political science (Fearon,
1995). Because states have private information about
their capabilities and resolve and lack the ability or will
to credibly transmit information about those factors to
obtain a better deal in negotiations, bargaining may
result in war. Commitment problems arise when states
anticipate that changing circumstances will lead any
bargain that they strike today to be unsustainable
tomorrow (Powell, 1999). As such, factors that help
reduce uncertainty and make processes of information
transmission more credible are helpful for reducing the
probability of war (e.g. Reed, 2003; Werner & Yuen,
2005; Rauchhaus, 2011). For instance, scholars have
focused on how factors such as the design of postwar
settlements (Mattes & Savun, 2010) can help conflict
from recurring in civil war.
Given these pervasive information and commitment
problems in IR, understanding the factors that reduce
uncertainty about an adversary’s capabilities and inten-
tions is a central priority for IR research. Some have
emphasized that states may attempt to use costly signals
2journal of PEACE RESEARCH XX(X)
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