Leader age and international conflict: A regression discontinuity analysis
| Published date | 01 July 2024 |
| DOI | http://doi.org/10.1177/00223433231201447 |
| Author | Andrew Bertoli,Allan Dafoe,Robert Trager |
| Date | 01 July 2024 |
https://doi.org/10.1177/00223433231201447
Journal of Peace Research
2024, Vol. 61(4) 643 –658
© The Author(s) 2023
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DOI: 10.1177/00223433231201447
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1225162JPR0010.1177/00223433231201447Journal of Peace ResearchBertoli et al.
research-article2023
Regular Article
Leader age and international conflict:
A regression discontinuity analysis
Andrew Bertoli
School of Politics, Economics & Global Affairs, IE University
Allan Dafoe
Centre for the Governance of AI
Robert Trager
Blavatnik School of Government, University of Oxford
Abstract
Does leader age matter for the likelihood of interstate conflict? Many studies in biology, psychology, and physiology
have found that aggression tends to decline with age throughout the adult lifespan, particularly in males. Moreover, a
number of major international conflicts have been attributed to young leaders, including the conquests of Alexander
the Great and the ambitious military campaigns of Napoleon. However, the exact nature of the relationship between
leader age and international conflict has been difficult to study because of the endogeneity problem. Leaders do not
come to power randomly. Rather, many domestic and international factors influence who becomes the leader of a
country, and some of these factors could correlate with the chances of interstate conflict. For instance, wary
democratic publics might favor older leaders when future international conflict seems likely, inducing a relationship
between older leaders and interstate conflict. This article overcomes such confounding by using a regression
discontinuity design. Specifically, it looks at close elections of national leaders who had large differences in age. It
finds that when older candidates barely defeated younger ones, countries were much less likely to engage in military
conflict. Its sample is also fairly representative of democracies more broadly, meaning that the findings likely hold
true for cases outside the sample. The results demonstrate the important role that individuals play in shaping world
politics. They also illustrate the value of design-based inference for learning about important questions in the study of
international relations and peace science.
Keywords
elections, international security, leaders, natural experiment, political psychology, regression discontinuity
In what ways are the foreign policies of states shaped by
the individuals who lead them? This question has played
a central role in the study of interstate politics going back
to Thucydides, who devoted great attention to leader
qualities and their apparent impact on state behavior
(Connor, 1984). This focus is perhaps most evident in
the contrast between the young, bold Alcibiades, who
favored war with Syracuse, and the older, cautious
Nicias, who opposed it.
In this article, we take up the question of whether
leader age matters for the likelihood of international
conflict. Focusing on democracies, we employ a regres-
sion discontinuity design that takes advantage of the as-if
random outcomes of very close elections between poten-
tial leaders with large differences in age. Our results
indicate that electing older leaders does make countries
less likely to act aggressively towards other states. We also
find that the estimated effect is much larger when
Corresponding author:
abertoli@faculty.ie.edu
644 journal of P R 61(4)
presidential democracies have united governments, pos-
sibly because leaders exercise greater influence over for-
eign policy when their co-partisans control the legislative
branch (Howell & Pevehouse, 2005, 2007). In addition,
our estimates are much larger for more consolidated
democracies, suggesting that leader traits matter more
when democratic leaders have greater political security
(Bueno de Mesquita et al., 1999; Chiozza & Goemans,
2003; Palmer, London & Regan, 2004).
These findings accord with many recent studies that
contain a wealth of evidence about the effects of leaders
on international conflict (e.g. Saunders, 2011; Weeks,
2014; Barcelo
´, 2020; Dube & Harish, 2020). Our
regression discontinuity design overcomes a key chal-
lenge that makes research on this topic difficult – the
endogeneity problem. Put simply, who comes to power
in a country is not random. It is influenced by many
factors at the domestic and international levels, and some
of these factors could correlate with the chances of inter-
state conflict. This can make it hard to know whether
differences in state behavior result from leaders them-
selves or from the broader circumstances that facilitated
their rise to power. Because we focus on close elections
where who became leader was essentially as-if random,
our estimates should be largely free of such selection
effects.
Our results also fit with the well-established finding in
other fields that aggression tends to decline over the adult
lifespan, particularly in males (Birditt & Fingerman,
2005; Williams et al., 2006; Neupert, Almeida &
Charles, 2007). Moreover, this conclusion receives fur-
ther support from the many international confrontations
that have been attributed to the desire of young leaders
to overturn the status quo. These cases range from the
wars of Alcibiades and Alexander the Great to the
23-year-old Austro-Hungarian Emperor Franz Josef’s
break with Russia during the Crimean War, a decision
he made against the strong advice of his 80-year-old elder
statesman, Prince Metternich (Rich, 1985; Trager,
2012). This disastrous decision that the emperor made
as a young man put him on the path to fight World War
I at the age of 83 because that early blunder precipitated
the security competition with Russia in the Balkans.
This article contributes to political science in several
important ways. First, the results provide strong evidence
from a natural experiment that leaders do have a signif-
icant independent impact on foreign policy. Recent
debates about medical research have made clear the great
value of research designs that have random or as-if ran-
dom treatment assignments for drawing causal infer-
ences. Such opportunities are rare in the study of
international conflict, but when they occur they can
provide very valuable insights into the factors that drive
state behavior (Jones & Olken, 2009; Dube & Harish,
2020). We thus believe that our article makes a very
important contribution in this regard. Our results
emphasize the importance of individual leader traits as
drivers of international outcomes and should encourage
more research in this area.
Second, our findings build a bridge between interna-
tional relations scholarship and a much broader body of
research about age and aggression that spans the fields of
biology, psychology, physiology, and criminology. This
is important because one of the primary goals of science
is to create unified bodies of knowledge, not just within
research programs but also between them. Our results
thus help create connections between scholarly fields that
can improve our understanding of human behavior more
broadly.
Third, our findings affirm the theory that youth may
partly explain why some notable leaders of the past have
launched aggressive military campaigns. For example,
the wars of Alexander the Great, Hannibal, Charle-
magne, Suleiman I, Gustavus Adolphus, Frederick the
Great, Napoleon, and Shaka may be partly explained by
how young these men were when they came to power.
Our findings should encourage historians and social
scientists to take leader age very seriously when investi-
gating the causes of international conflicts.
Age and aggression
The link between age and aggression has been well docu-
mented across many different cultural contexts (Daly &
Wilson, 1990; Steffensmeier & Streifel, 1991; Sweeten,
Piquero & Steinberg, 2013). Psychologists have demon-
strated that older adults adopt less aggressive strategies in
interpersonal relationships (Neupert, Almeida &
Charles, 2007; Hay & Diehl, 2011). All else equal, they
are less likely to yell or name call and more likely to
endorse withdrawing from conflictual situations.
Similarly, criminologists have described an ‘age-crime
curve’, according to which criminal behaviors rapidly
decline from late adolescence through young adulthood
and continue decreasing through old age (Farrington,
1986; Steffensmeier et al., 1989; MacLeod, Grove &
Farrington, 2012; Nyseth Brehm, Uggen & Gasanabo,
2016). The decline in crime with age seems to apply to
both violent and nonviolent types of crime (Steffensmeier
et al., 1989), and it continues as people in their 40s and
50s progress to their 60s and 70s (Steffensmeier et al.,
2journal of PEACE RESEARCH XX(X)
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