ETH Library
Horizontal Inequalities and
Ethnonationalist Civil War
A Global Comparison
Journal Article
Author(s):
Cederman, Lars-Erik; Weidmann, Nils B.; Gleditsch, Kristian Skrede
Publication date:
2011-08
Permanent link:
https://doi.org/10.3929/ethz-b-000160115
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In Copyright - Non-Commercial Use Permitted
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American Political Science Review 105(3), https://doi.org/10.1017/S0003055411000207
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American Political Science Review Vol. 105, No. 3 August 2011
doi:10.1017/S0003055411000207
Horizontal Inequalities and Ethnonationalist Civil War:
A Global Comparison
LARS-ERIK CEDERMAN ETH Z
¨
urich
NILS B. WEIDMANN Yale University
KRISTIAN SKREDE GLEDITSCH University of Essex
C
ontemporary research on civil war has largely dismissed the role of political and economic
grievances, focusing instead on opportunities for conflict. However, these strong claims rest on
questionable theoretical and empirical grounds. Whereas scholars have examined primarily the
relationship between individual inequality and conflict, we argue that horizontal inequalities between
politically relevant ethnic groups and states at large can promote ethnonationalist conflict. Extending
the empirical scope to the entire world, this article introduces a new spatial method that combines our
newly geocoded data on ethnic groups’ settlement areas with spatial wealth estimates. Based on these
methodological advances, we find that, in highly unequal societies, both rich and poor groups fight more
often than those groups whose wealth lies closer to the country average. Our results remain robust to a
number of alternative sample definitions and specifications.
A
lthough logistical and power-related
conditions—such as low state-level per capita
income, weak state institutions, and peripheral
and inaccessible territory—enjoy near-consensus sup-
port as explanations of civil war onset, most of the
contemporary literature regards explanations rooted
in political and economic grievances with suspicion
(Blattman and Miguel 2010). In fact, the debate over
the status of grievances in such explanations dates
back at least to the 1960s, with the introduction of
relative deprivation theory. Inspired by psychological
theories of conflict, Gurr (1970) and his colleagues
argued that economic and other types of inequality
increase the risk of internal strife through frustrated
expectations. In contrast, today’s most influential
quantitative studies of civil war give short shrift
Lars-Erik Cederman is Professor, Center for Comparative and In-
ternational Studies, Swiss Federal Institute of Technology (ETH)
Z
¨
urich, IFW D 49.2, 8092 Z
¨
urich, Switzerland (lcederman@ethz.ch).
Nils B. Weidmann is Postdoctoral Fellow, Jackson Institute for
Global Affairs, Yale University, P.O. Box 208206, New Haven, CT
06520 (nils.weidmann@yale.edu).
Kristian Skrede Gleditsch is Professor, Department of Govern-
ment, University of Essex, Wivenhoe Park, Colchester, Essex, UK
CO4 3SQ (ksg@essex.ac.uk).
All authors are also affiliated with Centre for the Study of Civil
War, PRIO, Oslo, Norway.
We thank the coeditors of the APSR, the anonymous reviewers,
Carles Boix, David Cunningham, Kathleen Cunningham, Erik Me-
lander, and Gudrun Østby for helpful comments and discussions, as
well as participants in seminars at the Centre for the Study of Civil
War, PRIO; the University of Arizona, the University of Z
¨
urich;
the Center of Comparative and International Studies, Z
¨
urich; the
University of Maryland; Yale University; and the 7th SGIR Pan-
European International Relations Conference, Stockholm. Christa
Deiwiks, Luc Girardin, and Julian Wucherpfennig offered crucial
research support. Cederman acknowledges support from the Eu-
ropean Science Foundation (06_ECRP_FP004) through the Swiss
National Science Foundation (105511-116795). Weidmann acknowl-
edges support from the Air Force Office of Scientific Research
(Grant FA9550-09-1-0314). Gleditsch acknowledges the support of
the European Science Foundation (06_ECRP_FP004) through the
Economic and Social Research Council (RES-062-23-0259) and the
Research Council of Norway (180441/V10).
to grievance-based accounts, based on reports that
unequal individual wealth distributions have no
statistically distinguishable relationship to internal
conflict (e.g., Collier and Hoeffler 2004; Fearon and
Laitin 2003).
Yet, despite these alleged nonfindings, the debate
over grievances is far from dead. Indeed, inequality
continues to occupy a prominent place in the qual-
itative literature on civil wars and has repeatedly
been linked to conflict processes (Sambanis 2005, 323;
Stewart 2008b; Wood 2003). Moreover, in the last few
years, some quantitative studies have started to appear
that argue that the current literature’s failure to con-
nect distributional asymmetries with conflict behavior
may actually be due to inappropriate conceptualization
and imperfect measurements, rather than reflecting a
fundamental absence of any causal effect (Østby 2008b;
see also Stewart 2008b).
Also relying on quantitative evidence, we join these
recent contributions in shifting the explanatory focus
from individualist to group-level accounts of inequal-
ity and conflict. Because formidable problems of data
availability associated with the uneven coverage and
comparability of surveys have stood in the way of
assessing such “horizontal inequalities” (HIs), most
scholars have had to content themselves with selective
case studies or statistical samples restricted to particu-
lar world regions.
To overcome these difficulties, we combine our
newly geocoded data on politically relevant ethnic
groups’ settlement areas with Nordhaus’s (2006) spa-
tial wealth measures, both with global coverage. Based
on this novel strategy, we present the first truly world-
wide comparison of horizontal inequality and ethnona-
tionalist civil wars. Controlling for political power ac-
cess, we show that both advanced and backward ethnic
groups are more likely to experience such conflict than
groups whose wealth lies closer to the national average.
Moreover, in agreement with a broad conception of
horizontal inequalities, we find that both political and
economic inequalities contribute to civil war. Extensive
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American Political Science Review Vol. 105, No. 3
sensitivity analysis confirms that our findings are robust
to various model specifications, alternative inequality
measures, and sample definitions.
We proceed as follows: First, we review the extensive
literature on inequality and conflict before narrowing
down the scope to our own theoretical framework,
which connects HIs with collective violence through
grievance-based mechanisms. Based on this approach,
we derive our main hypotheses on the effect of HIs
on civil war onset. To test the hypotheses, we then
introduce the datasets and describe our spatial method
of wealth estimation in detail, including how to use
the contours of the ethnic groups’ settlement areas as
“cookie cutters,” which allows us to extract the rel-
evant wealth estimates from the spatial wealth map.
After specifying the variables used in our empirical
analysis, we then expose the hypotheses to systematic
tests in the main models, followed by another section
that assesses the robustness of our findings. Finally,
concluding at least tentatively that both economic and
political inequality at the group level increase the risk
of ethnonationalist civil war, we argue that the civil
war literature’s tendency to downplay the importance
of grievances as a source of internal conflict is both
premature and misguided.
INEQUALITY IN THE CIVIL WAR
LITERATURE
Intimately related to issues of power and wealth dis-
tribution in society, inequality plays a central role in
classical theories of conflict. In an influential article,
Davies (1962) argued that revolutions were motivated
by frustration resulting from an evolving gap between
individual aspirations and actual economic status. Also
adopting an explicitly psychological perspective, Gurr’s
(1970) well-known theory of relative deprivation char-
acterizes various types of collective violence as reac-
tions to frustrations stemming from unfulfilled aspira-
tions, usually related to material well-being (see review
in Brush 1996). Such a perspective differs radically
from earlier sociological theories of mob behavior that
explained collective violence as a societal pathology
(e.g., Le Bon 1913). Instead, relative deprivation theo-
rists argue that individuals’ widespread discontent with
their social situation triggers conflict, especially where
modernization fuels a “revolution of rising expecta-
tions” (Davies 1962).
Although related indirectly to inequality through
this psychological mechanism, relative deprivation the-
ory does not explicitly focus on interpersonal or inter-
group wealth comparisons (Hogg and Abrams 1988;
Regan and Norton 2005; cf. Gurr and Duvall 1973).
Other theories adopt a structural perspective, linking
various types of inequality explicitly to structural im-
balances in society, such as uneven income or land dis-
tribution (Acemo
˘
glu and Robinson 2005; Muller 1985;
Muller and Seligson 1987; Russett 1964). Partly un-
der the inspiration of Marxist principles, the literature
on peasant rebellions explains violent collective action
as a response to unequal wealth allocation (Moore
1966; Scott 1976). Frustrated with their lot, the peasant
masses and other underprivileged groups are expected
to take up arms as a way to seize power and redistribute
wealth in their favor.
Relative deprivation theory remains perhaps the
most prominent explanation that connects grievances
with conflict, but has a very mixed record as regards em-
pirical evidence (Brush 1996; Oberschall 1978). Early
on, the theory attracted criticism from Snyder and
Tilly (1972), who argued that opportunity-based mobi-
lization rather than grievances causes internal conflict
and revolutions. Contending that all societies contain
a number of aggrieved and frustrated individuals, they
did not think “there is any general connection between
collective violence and hardship such that an observer
could predict one from the other” (Tilly 1972, 520; see
also Skocpol 1979; Tilly 1978). Along similar lines, a
series of studies challenged the results pertaining to
income inequality, which was usually seen as closely
connected to the notion of relative deprivation (see,
e.g., Weede 1987). By the end of the 1980s, the de-
bate remained unresolved, with virtually all possible
causal connections—negative, positive, curvilinear, or
none—being represented in the literature (Lichbach
1989).
As the end of the Cold War brought with it a new
wave of conflict, most of which was ethnonationally
motivated, Gurr (1993, 2000a, 2000b) extended his
previous theory and began to study ethnic minorities’
reactions to state-imposed disadvantages and discrim-
ination. In agreement with Horowitz’ (1985) seminal
study of ethnic groups in conflict, Gurr found that
ethnic grievances contributed indirectly to collective
violence through ethnic mobilization.
In contrast, the contemporary civil war literature has
been pioneered by scholars who take issue with such
reasoning. Positioning themselves explicitly against
grievance-based theories in political science and sociol-
ogy, Collier and Hoeffler (2004) follow in the footsteps
of earlier critics of relative deprivation (although with-
out referring to them explicitly). Very much as Snyder
and Tilly had done three decades earlier, Collier and
Hoeffler (2004, 564) point to the ubiquity of frustra-
tion around the world, asserting that this fact deprives
the theory of explanatory value: “Misperceptions of
grievances may be very common: All societies may
have groups with exaggerated grievances. In this case,
as with greed-rebellion, motive would not explain the
incidence of rebellion.” Explicitly classifying inequali-
ties as grievance-related indicators, these authors rely
on the Gini coefficient to measure the income distri-
bution among individuals. Having found no statistical
effect for this and other hardship proxies, Collier and
Hoeffler feel vindicated in their wholesale rejection of
grievances and inequality as causes of civil war. In his
best-selling book The Bottom Billion, Collier (2007, 18)
confirms these doubts:
So what causes civil war? Rebel movements themselves
justify their actions in terms of a catalogue of grievances:
repression, exploitation, exclusion. Politically motivated
academics have piled in with their own hobbyhorses, which
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Horizontal Inequalities and Civil War August 2011
usually cast rebels as heroes. I have come to distrust this
discourse of grievances as self-serving.
1
In another influential study that stresses political
and institutional causes of civil war, Fearon and Laitin
(2003) present findings that cast doubt on ethnic and
political grievances as explanations of conflict onset.
Like Collier and Hoeffler, Fearon and Laitin rely on
a series of individual-level statistical proxies, includ-
ing the Gini coefficient, which provide no evidence
of economic inequality increasing the risk of conflict.
Summing up these and other studies, Laitin (2007, 23)
concludes that
ethnic grievances are commonly felt and latent; the factors
that make these grievances vital and manifest differentiate
the violent from the nonviolent cases. Ex ante measures of
grievance levels are not good predictors of the transforma-
tion of latent grievances into manifest ones. And it is the
factors that turn latent grievances into violent action that
should be considered as explanatory for that violence.
Despite these negative findings, a number of schol-
ars find the rejection of grievances and inequalities
premature. Although the poor quality of distributional
economic data within and across countries should per-
haps be reason for pause by itself,
2
the main reason
that grievance-based arguments cannot be so easily re-
jected is that these studies largely miss their theoretical
target. Insisting that conflict-inducing inequality can-
not be reduced to household-level measures of income
distribution such as the Gini coefficient, Cramer (2003)
calls for an alternative that is explicitly relational and
theoretically grounded.
3
In the concluding chapter of a
two-volume compilation of case studies testing Collier
and Hoeffler’s (2004) model, Sambanis (2005) draws
the same inference. Noting that there is a major dis-
crepancy between the quantitative nonfinding and the
repeated references to inequality in the case studies,
Sambanis (2005, 324) considers a number of explana-
tions, including problems relating to interpretation and
sampling of case evidence, as well as the fundamental
issue of aggregation level:
There may exist a relationship between inequality and
popular revolutions or class conflict, which is another rea-
son to consider disaggregating the cases of civil war. But
ethnic or secessionist wars should, in theory, be driven
more by group-based inequality . . . than by interpersonal
inequality.
A more promising way to capture the link between
uneven wealth distributions and conflict has been pro-
posed by Stewart (2008b) and her colleagues, who
1
In more recent research, Collier, Hoeffler, and Rohner (2009)
maintain that civil wars are caused by factors associated with “feasi-
bility” rather than by grievances and other types of motivations.
2
Using a different conceptualization of vertical inequality condi-
tioned on factor mobility, Boix (2008) reports a strong effect on
internal conflict.
3
Likewise arguing against misplaced individualism, Cederman and
Girardin (2007) criticize the use of the ethnolinguistic fractionaliza-
tion index as a general proxy for ethnonationalist frustration.
contrast vertical, or individual-level inequalities, with
horizontal inequalities. Defining the latter as “inequal-
ities in economic, social or political dimensions or cul-
tural status between culturally defined groups,” Stew-
art (2008a, 3) argues that to a large extent, scholars
have failed to find evidence of inequality’s war-causing
effect because of their reliance on individualist, rather
than group-based, measures of income and power dif-
ferences:
But the majority of internal conflicts are organized group
conflicts—they are neither exclusively nor primarily a mat-
ter of individuals committing acts of violence against oth-
ers. What is most often involved is group mobilization of
people with particular shared identities or goals to attack
others in the name of the group. (Stewart 2008a, 11)
Following the lead of Horowitz and Gurr, Stewart
(2008a) conceptualizes horizontal inequality broadly
by considering political, economic, social, and cultural
dimensions explicitly. Political HIs entail blocked or
limited access to central decision-making authority
within the state. The economic dimension taps the dis-
tribution of wealth among households. Social HI mea-
sures primarily groups’ uneven social access, for exam-
ple, in terms of education and societal status. Finally,
the cultural aspect captures group-level inequalities
with respect to cultural policies and symbols, including
national holidays and religious rights.
Recognizing the difficulties of measuring HIs, Stew-
art’s team has so far primarily relied on case stud-
ies rather than large-N comparisons. The picture that
emerges from this research suggests that both disad-
vantaged and advanced groups have a higher likeli-
hood of getting involved in internal conflict than groups
closer to the country average (Stewart 2008b). Yet
some quantitative researchers have attempted to gen-
eralize from the case studies to a larger set of countries.
In a pioneering statistical test, Barrows (1976) detected
an influence of group-level differences on conflict in
sub-Saharan Africa. Relying on household surveys
conducted in 39 developing countries, Østby (2008b)
finds evidence that social horizontal inequality causes
civil war, although the economic dimension appears
to be weaker (see also Østby 2008a). In a follow-up
study based on geocoded conflict and survey data from
sub-Saharan Africa, Østby, Nord
˚
as, and Rød (2009)
reach firmer conclusions, showing that both economic
and social group-level differences are likely drivers of
conflict behavior.
THEORIZING HORIZONTAL INEQUALITIES
We now turn to our own account of inequality and
conflict. The starting point of our approach to ethnona-
tionalist warfare is the realization that ethnic groups
find themselves in radically different situations for var-
ious historical reasons. Whereas some ethnic groups
came out on top of the geopolitical game, others were
conquered early on, and therefore lost out in the com-
petition for wealth and influence. Moreover, the un-
even spread of nationalism delayed mass-level political
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American Political Science Review Vol. 105, No. 3
mobilization in many parts of the world, thus creating
differences in both economic and political develop-
ment that were often exploited by alien rulers (Gellner
1964). As argued by Tilly (1999), nationalism can be
thought of as a case of “categorical inequality” because
it asserts and creates paired and unequal categories, either
(a) rival aspirants to nationhood or (b) members of the
authentic nation versus others. It involves claims to prior
control over a state, hence to the exclusion of others from
that priority. It authorizes agents of the nation to subor-
dinate, segregate, stigmatize, expel, or even exterminate
others in the nation’s name. (172)
Adopting Stewart’s definition of HI, we focus on the
political and economic dimensions of HI.
4
Although
these two types of inequality are often likely to be
related, we follow Stewart in treating the distribu-
tion of power and of wealth as conceptually separate
components. Previous quantitative research has exam-
ined the role of political exclusion of ethnic groups on
the risk of civil war, but has not considered explicitly
the economic aspect of exclusion and the relationship
between the two (see e.g., Cederman, Buhaug, and
Rød 2009; Cederman and Girardin 2007; Cederman,
Wimmer, and Min 2010; though see Gurr 1993, 2000b).
By contrast, some critics of the role of ethnicity, such
as Woodward (1995), argue that alleged ethnic conflicts
are really driven by underlying economic inequalities
that lead ethnic identities to become politicized. A
strong version of this argument would hold that ethnic
political inequalities are irrelevant in the absence of
economic inequalities.
Building on our previous work, we view HIs as struc-
tural asymmetries that make ethnonationalist civil war
more likely and adopt an indirect research strategy that
explains the effect of inequality by postulating a set of
causal mechanisms. To close the gap between the struc-
tural background conditions and behavioral patterns,
we propose intermediate analytical steps.
5
First, we
postulate that objective political and economic asym-
metries can be transformed into grievances through a
process of group comparison driven by collective emo-
tions. Second, we argue that such grievances trigger
violent collective action through a process of group
mobilization.
From Horizontal Inequalities to Grievances
As opposed to objective conditions such as horizontal
inequalities, grievances are intersubjectively perceived
phenomena. As we have noted earlier in the text, this
makes them very hard to measure, but we can draw
on an extensive experimentally supported literature
4
As we have seen, HIs also involve social and cultural policies (see
Stewart 2008a). We acknowledge that these aspects may be linked to
conflict, but these conflict mechanisms fall outside the scope of this
article.
5
See Gurr (2000b, Chap. 3) for a similar theory based on four
conditions, namely the salience of ethnocultural identity, collective
incentives for action, collective-action capacity, and environmental
opportunities.
in social psychology as a way to construct plausible
mechanisms connecting structural asymmetries with
collective violence. Obviously, it may be possible to find
ways to connect HIs with conflict through causal mech-
anisms that do not feature grievances, but we leave this
possibility to other researchers to explore.
6
Before grievances can be acted upon, they need to
be cognitively linked to social identities through self-
categorization (Hogg and Abrams 1988, 21). Clearly
the salience of ethnic distinctions varies over time and
from case to case (Gurr 2000b), but once group iden-
tities become salient, members of the involved groups
are prone to make social comparisons that hinge on the
distinction between in-group and out-group categories
(Turner 1981). According to “realistic conflict theory,”
conflicting claims to scarce resources, including power,
prestige, and wealth, are likely to produce ethnocen-
tric and antagonistic intergroup relations (Tajfel and
Turner 1979). In stratified social systems, social compar-
ison reflecting superiority or inferiority should be es-
pecially likely to trigger conflict (see Horowitz 1985).
7
These processes of social comparison and intergroup
evaluation are far from emotionally neutral. As argued
by Kalyvas (2006) and Petersen (2002), attempts to
reduce the violent excesses of civil wars to entirely
calculative and cognitive processes fly in the face of
countless testimonies of the emotional escalation pro-
cesses leading to the outbreak of collective violence.
8
In particular, violations of norms of justice and equal-
ity will typically arouse feelings of anger and resent-
ment among members of the disadvantaged group.
9
As observed in a pioneering study by T. H. Marshall,
such emotional responses are present in class systems,
which “are based structurally on chronic asymmetries
of power and reward” (Barbalet 1992, 153).
What is true for cases of class resentment also ap-
plies to inequalities among ethnic groups. In agreement
with Petersen (2002), we postulate that resentment
based on intergroup comparisons involving HIs often
6
It should be noted that the presence of HIs presupposes the ex-
istence of well-defined groups (Stewart 2000), which is not a trivial
precondition (e.g., Kalyvas 2006). Although it is undoubtedly true
that modern politics is to a large extent group-based, and social life
hinges on social categories (Gellner 1964; Hogg and Abrams 1988),
we argue that the extent to which cohesive groups can actually be
said to exist is ultimately a matter of empirical analysis. Yet, be-
cause our goal is to evaluate the conflict-inducing effect of HIs, we
join Horowitz (1985), Gurr (1993; 2000b) and others in adopting
a self-consciously group-based framework, although restricting our
substantive focus to groups defined through ethnic categorization
rather than through other cleavages.
7
In addition to such direct consequences of objective differences,
“social identity theory” tells us that mere awareness of social out-
groups may be sufficient to provoke competitive behavior even in the
absence of objective issues of contention (Tajfel and Turner 1979).
8
Indeed, although social identity theorists stress the cognitive com-
ponent of group behavior, they allow for an important element of
emotional engagement, as group membership is assumed to be inti-
mately associated with self-esteem (Hogg and Abrams 1988).
9
Modern sociological theories of emotions tell us that, contrary to
the views of early crowd theorists, and contrary to lingering popular
belief, emotions are not irrational, but serve distinctly goal-directed
purposes in social and political life (e.g., Emirbayer and Goldberg
2005; Petersen 2002).
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