¹ ‘Sri Lanka military, rebels trade death toll claims’, Reuters India (Colombo: Reuters, 1 March 2008).

² Collier, Paul and Hoeffler, Anke, ‘Greed and Grievance in CivilWar’, World Bank Policy Research Working Paper, No. 2355 (2000)Google Scholar; Fearon, J. D. and Laitin, D. D., ‘Ethnicity, Insurgency, and Civil War’, American Political Science Review, 97 (2003), 75–90CrossRefGoogle Scholar; Montalvo, J. G. and Reynal-Querol, M., ‘Ethnic Polarization, Potential Conflict, and Civil Wars’, American Economic Review, 95 (2005), 796–816CrossRefGoogle Scholar.

³ Lipset, Seymour Martin, Political Man: The Social Bases of Politics (Garden City, N.Y.: Doubleday, 1960)Google Scholar.

⁴ Lipset, Political Man; Rae, Douglas W. and Taylor, Michael, The Analysis of Political Cleavages (New Haven, Conn.: Yale University Press, 1970)Google Scholar.

⁵ Muni, S. D., ‘Ethnic Conflict, Federalism, and Democracy in India’, in Kumar Rupesinghe and Valery A. Tishkov, eds, Ethnicity and Power in the Contemporary World (New York: United Nations University Press, 1996)Google Scholar.

⁶ Collier, Paul, Hoeffler, Anke and Rohner, Dominic, ‘Beyond Greed and Grievance: Feasibility and Civil War’ (Oxford: Centre for the Study of African Economies, Working Paper Series, 1996)Google Scholar.

⁷ Collier and Hoeffler, ‘Greed and Grievance in Civil War’.

⁸ Fearon and Laitin, ‘Ethnicity, Insurgency, and Civil War’.

⁹ Urdal, Henrik, ‘A Clash of Generations? Youth Bulges and Political Violence’, International Studies Quarterly, 50 (2006), 607–629CrossRefGoogle Scholar.

¹⁰ Cederman, Lars-Erik, Rød, Jan Ketil and Weidmann, Nils, ‘Geo-Referencing of Ethnic Groups: Creating a New Dataset’, in GROW Workshop (Oslo: Peace Research Institute (PRIO), 2006)Google Scholar.

¹¹ Chai refers to this as in-group altruism; see Chai, Sun-Ki, ‘A Theory of Ethnic Group Boundaries’, Nations and Nationalism, 2 (1996), 281–307CrossRefGoogle Scholar.

¹² Chwe, Michael Suk-Young, Rational Ritual: Culture, Coordination, and Common Knowledge (Princeton, N.J.: Princeton University Press, 2001)Google Scholar.

¹³ Granovetter, M., ‘The Impact of Social Structure on Economic Outcomes’, Journal of Economic Perspectives, 19 (2005), 33–50CrossRefGoogle Scholar.

¹⁴ Cederman, L. E. and Girardin, L., ‘Beyond Fractionalization: Mapping Ethnicity onto Nationalist Insurgencies’, American Political Science Review, 101 (2007), 173–185CrossRefGoogle Scholar.

¹⁵ Cederman and Girardin, ‘Beyond Fractionalization’.

¹⁶ I use the broader term social structure to refer to a description of macro social cleavages and groups including characteristics of individual cleavages and/or groups as well as the relationship of cleavages to each other.

¹⁷ A cleavage is a ‘division on the basis of some criteria of individuals, groups, or organizations [between] whom conflict may arise’ ( Lane, Jan-Erik and Ersson, Svante O., Politics and Society in Western Europe (London: Sage, 1994)Google Scholar.

¹⁸ Horowitz, Donald L., Ethnic Groups in Conflict (Berkeley: University of California Press, 1985)Google Scholar.

¹⁹ Fox, Jonathan, Religion, Civilization, and Civil War: 1945 through the Millennium (Lanham, Md.: Lexington Books, 2004)Google Scholar.

²⁰ Collier, Paul and Hoeffler, Anke, ‘On Economic Causes of Civil War’, Oxford Economic Papers, 50 (1998), 563–573CrossRefGoogle Scholar; Collier, and Hoeffler, , ‘Greed and Grievance in Civil War’, World Bank Policy Research Working Paper, No. 2355Google Scholar; Collier, Paul and Hoeffler, Anke, ‘Greed and Grievance in Civil War’, Oxford Economic Papers, 56 (2004), 563–595CrossRefGoogle Scholar.

²¹ In other work, I have used a cross-cutting index of ethnicity and income to try and measure this. See Selway, Joel and Gubler, Joshua, ‘Ethno-Income Inequality, Ethno-Geographic Dispersion, Ethno-Religious Cross-Cuttingness and Civil War Onset’ (unpublished paper)Google Scholar.

²² Cederman, Rød and Weidmann, ‘Geo-Referencing of Ethnic Groups’.

²³ All the previously cited cleavages have been or can be further dissected: ethnicity into race and language, religion into sects and denominations, and geography into region, rural/urban residence and centre/periphery.

²⁴ I explicitly separate the two cleavages as distinct, while recognizing that much recent work on ethnicity incorporates religion into a broader definition of ethnicity. See: Varshney, A., Ethnic Conflict and Civic Life (New Haven, Conn.: Yale University Press, 2002)Google Scholar; Chandra, K., Why Ethnic Parties Succeed (Cambridge: Cambridge University Press, 2004)CrossRefGoogle Scholar; Posner, Daniel N., ‘Measuring Ethnic Fractionalization in Africa’, American Journal of Political Science, 48 (2004), 849–863CrossRefGoogle Scholar. This decision comes with trade-offs, most important of which is that in countries where ethnicity and religion seem virtually inseparable, such as Malaysia, we cannot know whether a measure of cross-cuttingness is meaningful. More broadly, we can categorize this in the long-standing challenge of measuring the salience of cleavages in society.

²⁵ Rae and Taylor, The Analysis of Political Cleavages.

²⁶ Horowitz, Ethnic Groups in Conflict; Fox, Religion, Civilization, and Civil War.

²⁷ There is a growing sociological literature, under the rubric of the ‘religious economy’, which argues that switching religions (especially denominations within religions) is more common than many think. In my dataset, for most of the countries that appeared in more than one survey over time, there appeared to be minimal changes in the scores. On the whole, this supports my assertion that religious and ethnic identity are difficult, though not impossible, to change, especially when they are the bases for conflict.

²⁸ A group is a category of identity/membership within a single cleavage, such as Christian and Muslim within the religion cleavage.

²⁹ Scarritt, James R. and Mozaffar, Shaheen, ‘The Specification of Ethnic Cleavages and Ethnopolitical Groups for the Analysis of Democratic Competition in Contemporary Africa’, Nationalism & Ethnic Politics, 5 (1999), 82–117CrossRefGoogle Scholar; Posner, ‘Measuring Ethnic Fractionalization in Africa’; Cederman and Girardin, ‘Beyond Fractionalization’.

³⁰ Stoll, Heather, ‘Social Cleavages, Political Institutions, and Party Systems: Putting Preferences Back into the Fundamental Equation of Politics’, Political Science (Palo Alto, Calif.: Stanford University, 2004)Google Scholar.

³¹ Posner, , ‘Measuring Ethnic Fractionalization in Africa’, p. 853Google Scholar.

³² Easterly and Levine, for example, use the terms ethnic diversity, polarization and ethnic fractionalization almost interchangeably in their path-breaking study on how ethnicity affects economic growth. See: Easterly, W. and Levine, R., ‘Africa’s Growth Tragedy: Policies and Ethnic Divisions’, Quarterly Journal of Economics, 112 (1997), 1203–1250CrossRefGoogle Scholar.

³³ Many scholars have used some variation of the Herfindahl index of fractionalization to measure the effective number of ethnic or religious groups in a society. Specifically, , where p_i is the proportion of society that identifies with a given ethnic group.

³⁴ Reynal-Querol, M., ‘Ethnicity, Political Systems, and Civil Wars’, Journal of Conflict Resolution, 46 (2002), 29–54CrossRefGoogle Scholar. Reynal-Querol actually uses the term polarization, which has often been used in the political science literature to describe the cultural distance between groups on a given cleavage. She uses the equation , where p_i is again the proportion of society that identifies with a given ethnic group. While this equation is similar to Esteban and Ray’s measure of polarization, Reynal-Querol imposes an assumption that the distance, or intensity of difference, between any pair of groups is identical. In other words, cultural distance is already contained in the underlying assumption. To avoid confusion with cultural polarization, I use the term bipolarization, since the measure is maximized with two groups (or two poles) of equal size. See: Esteban, J. M. and Ray, D., ‘On the Measurement of Polarization’, Econometrica, 62 (1994), 819–851CrossRefGoogle Scholar.

³⁵ Montalvo and Reynal-Querol, ‘Ethnic Polarization, Potential Conflict, and Civil Wars’; Easterly and Levine, ‘Africa’s Growth Tragedy’.

³⁶ Collier and Hoeffler, ‘Greed and Grievance in Civil War’.

³⁷ Fearon and Laitin, ‘Ethnicity, Insurgency, and Civil War’.

³⁸ Montalvo and Reynal-Querol, ‘Ethnic Polarization, Potential Conflict, and Civil Wars’.

³⁹ Hegre, H. and Sambanis, N., ‘Sensitivity Analysis of Empirical Results on Civil War Onset’, Journal of Conflict Resolution, 50 (2006), 508–535CrossRefGoogle Scholar.

⁴⁰ Quinn, Kevin, Hechter, Michael and Wibbels, Erik, ‘Ethnicity, Insurgency, and Civil War Revisited’ (paper presented at Laboratory in Comparative Ethnic Processes (LICEP) meeting, 2004)Google Scholar.

⁴¹ Collier and Hoeffler, ‘Greed and Grievance in Civil War’. Annett also offers a measure of social fractionalization, which captures fractionalization on both the religious and ethnic cleavages - defined as one half times the value of ethnic fractionalization plus one half times the value of religious fractionalization. To date, I have not seen this measure used in a study of civil war. See Annett, Anthony, ‘Social Fractionalization, Political Instability, and the Size of Government’, IMF Staff Papers, 48 (2001)Google Scholar.

⁴² Frisby, David and Schroeter, Gerd, ‘George Simmel: Review’, Canadian Review of Sociology and Anthropology, 23 (1986), p. 285Google Scholar.

⁴³ This term is my own. Past references to this same characteristic/phenomenon include cross-cutting cleavages, cross-cutting circles, criss-cross pattern of cleavage structure and intersection of cleavages. The antonym (reinforcing) has also been referred to as overlapping cleavages, consolidation of cleavages, superimposition of lines of differentiation and correspondence of cleavages.

⁴⁴ Blau, Peter Michael and Schwartz, Joseph E., Crosscutting Social Circles: Testing a Macrostructural Theory of Intergroup Relations (Orlando, Fla.: Academic Press, 1984), p. 83Google Scholar.

⁴⁵ Beteille, A., ‘A Brief Note on the Role of Cross-Cutting Alliances in Segmentary Political Systems’, Man, 60 (1960), 181–182CrossRefGoogle Scholar.

⁴⁶ Evans-Pritchard, E., ‘The Nuer of the Southern Sudan’, in M. Fortes and E. Evans-Pritchard, eds, African Political Systems (London: Oxford University Press, 1940), pp. 272–296Google Scholar.

⁴⁷ Gluckman, Max, ‘Political Institutions’, in E. E. Evans-Pritchard, ed., The Institutions of Primitive Society (Glencoe, Ill.: The Free Press, 1954), pp. 66–80Google Scholar.

⁴⁸ Kroeber, A. L., Zũni Kin and Clan (New York: The Trustees of the American Museum of Natural History, 1917), p. 183Google Scholar.

⁴⁹ Truman, David Bicknell, The Governmental Process: Political Interests and Public Opinion (New York: Knopf, 1951)Google Scholar.

⁵⁰ Rae and Taylor, The Analysis of Political Cleavages.

⁵¹ Lipset, Political Man.

⁵² Alan Dahl, Robert, A Preface to Democratic Theory (Chicago: University of Chicago Press, 1956)Google Scholar.

⁵³ Selway, Joel, ‘Cross-cutting Cleavages: Theory and Measurement of Social Structure’ (unpublished paper)Google Scholar.

⁵⁴ Rae and Taylor, The Analysis of Political Cleavages.

⁵⁵ In between the individual and cleavage levels of analysis is the group-level dynamic. Cross-fragmentation, furthermore, dissolves in-groups and diminishes group pressures. To motivate measures of cross-cuttingness, I thus pose the question: ‘In what way should groups on a cleavage x be distributed amongst groups on a second cleavage y to maximize cross-cuttingess?’ This question motivates at least two additional measures – cross-proportionalization and cross-bipolarization – and indeed is able to motivate our first two measures also. Indices for these measures have not yet been computed, but are forthcoming. See Selway, ‘Cross-cutting Cleavages’.

⁵⁶ Blau and Schwartz, Crosscutting Social Circles.

⁵⁷ Lipset, Political Man.

⁵⁸ Rae and Taylor, The Analysis of Political Cleavages.

⁵⁹ Since the statistics literature is unclear on which measure is superior, I opt for the more widely used Cramer’s V. See: Agresti, Alan, Categorical Data Analysis (New York: Wiley-Interscience, 2002)CrossRefGoogle Scholar.

⁶⁰ O stands for the observed frequencies in a simple cross-tabulation of the religious and ethnic cleavages; E stands for expected frequencies, calculated by multiplying the two marginal frequencies from the original cross-tabulation; i refers to cells in the contingency table.

⁶¹ However, neither heterogeneity nor sub-group fractionalization are sensitive to group identity on both cleavages, and thus do not capture cross-cuttingness. A simple example illustrates why sub-group fractionalization is not a measure of cross-cuttingness. Consider Society A with its two ethnic groups, black and white, each composing 50 per cent of the population, and its two religions, Christian and Muslim, each also composing 50 per cent of the population. The sub-group fractionalization score for Society A is 0.5. In a second society, B, we could have a society with the same sub-group fractionalization score, 0.5, but with a huge difference in the structure of its cleavages. Specifically, in Society B, there is just one ethnic group split 50–50 between religions. We can thus see where subgroup fractionalization fails to capture the concept of cross-cuttingness: it is not sensitive to the identities of the groups that compose the subgroups. Selway identifies this as a cross-cuttingness axiom. See Selway, ‘Cross-cutting Cleavages’.

⁶² Collier and Hoeffler imply that this relationship should be interactive also. See Collier, and Hoeffler, , ‘Greed and Grievance in Civil War’, p. 570Google Scholar.

⁶³ Inglehart, Ronald and Welzel, Christian, Modernization, Cultural Change and Democracy: The Human Development Sequence (New York: Cambridge University Press, 2005)CrossRefGoogle Scholar.

⁶⁴ See Papacostas, Antonis, Eurobarometer 63.4: European Union Enlargement, the European Constitution, Economic Challenges, Innovative Products and Services, May–June 2005 [Computer file]Google Scholar; Soufflot de Magny, R., Eurobarometer 63.3 Lifelong Learning in the Ten New European Union Member Countries and Consumer Rights in Poland, March–April 2005 [Computer file]Google Scholar; Reif, Karlheinz and Cunningham, George, Central and Eastern Euro-barometer 3: Political Disintegration, October–November 1992 [Computer file]Google Scholar.

⁶⁵ The AfroBarometer, http://www.afrobarometer.org.

⁶⁶ The AmericasBarometer by the Latin American Public Opinion Project (LAPOP), http://www.vanderbilt.edu/lapop/HOME. We thank the Latin American Public Opinion Project (LAPOP) and its major supporters (the United States Agency for International Development, the United Nations Development Program, the Inter-American Development Bank and Vanderbilt University) for making the data available.

⁶⁷ Takashi Inoguchi et al., AsiaBarometer Survey Data (2003 or 2004) [computer file]. AsiaBarometer Project (http://www.asiabarometer.org/) [producer and distributor], Accessed December 2006. AsiaBarometer is a registered trademark of Professor Takashi Inoguchi, Chuo University, Japan, Director of the AsiaBarometer Project, Room 2137, Building Two, Chuo University, Korakuen Campus, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan.

⁶⁸ The Comparative Study of Electoral Systems (www.cses.org).

⁶⁹ Andrews, Gary R., World Health Organization Collaborative Study on Social and Health Aspects of Aging in Fiji, Korea, Malaysia, and the Philippine (1983–5). [Computer file]Google Scholar; Andrews, Gary R, World Health Organization Regional Office for Southeast Asia Collaborative Study on Social and Health Aspects of Aging in Burma, Indonesia, North Korea, Sri Lanka, and Thailand (1990) [Computer file]Google Scholar; Andrews, Gary R., World Health Organization Collaborative Study on Social and Health Aspects of Aging in Bahrain, Egypt, Jordan, and Tunisia (1991) [Computer file]Google Scholar.

⁷⁰ Appendix available at author’s website, http://www.umich.edu/~jselway.

⁷¹ See author’s website http://www.umich.edu/~jselway.

⁷² The raw data, including tables from these analyses, will eventually be available at the author’s website http://www.umich.edu/~jselway.

⁷³ This comparison was necessarily restricted to African countries, and thus the Afrobarometer and World Values Survey, since Posner’s index concentrates on Africa. The results are nevertheless encouraging. See: Posner, ‘Measuring Ethnic Fractionalization in Africa’. Full analysis is available in the appendix at http://www.umich.edu/~jselway.

⁷⁴ There may be additional problems of representativeness in terms of the self-selection bias inherent in the types of surveys I am using. While this may exclude countries that have recently experienced civil war, the data go back far enough to diminish this problem.

⁷⁵ IMF, ‘World Economic Outlook Database’ (Washington, D.C.: International Monetary Fund, 2007)Google Scholar.

⁷⁶ Fearon and Laitin, ‘Ethnicity, Insurgency, and Civil War’.

⁷⁷ See Beck, Nathaniel, Katz, Jonathan N. and Tucker, Richard, ‘Taking Time Seriously: Time-Series-Cross-Section Analysis with a Binary Dependent Variable’, American Journal of Political Science, 42 (1998), 1260–1288CrossRefGoogle Scholar. I also experiment with two alternative ways to control for time dependence. First, I use a lagged variable for the occurrence of war as Fearon and Laitin do (see Fearon and Laitin, ‘Ethnicity, Insurgency, and Civil War’). In addition, I follow Hegre et al.’s method of using a variable that assumes that the effect of a previous conflict is decaying over time according to the formula exp{(-peace years)/X}, where ‘peace years’ is the number of years since a country experienced a civil war (see Hegre and Sambanis, ‘Sensitivity Analysis of Empirical Results on Civil War Onset’. The value X determines the rate of decay. I follow Toset et al. and set X to 4, implying that the risk of civil war is halved approximately every 3 years (see Toset, H. P. W., Gleditsch, N. P. and Hegre, H., ‘Shared Rivers and Interstate Conflict’, Political Geography, 19 (2000), 971–996CrossRefGoogle Scholar. This decaying variable takes on values close to 1 immediately after the end of a conflict and approaches 0 over time. The major results are not appreciably affected by these various approaches.

⁷⁸ Gleditsch, N. P., Wallensteen, P., Eriksson, M., Sollenberg, M. and Strand, H., ‘Armed Conflict 1946–2001: A New Dataset’, Journal of Peace Research, 39 (2002), 615–637CrossRefGoogle Scholar. Sometimes referred to as the ‘Armed Conflict Data’, the PRIO data I use were restricted to conflicts with at least 1,000 battle deaths by Urdal. I thank him for his generous sharing of data (see Urdal, ‘A Clash of Generations?’).

⁷⁹ Appendix available at http://www.umich.edu/~jselway.

⁸⁰ Collier, and Hoeffler, , ‘Greed and Grievance in Civil War’, Oxford Economic Papers, 56 (2004)CrossRefGoogle Scholar.

⁸¹ Collier, and Hoeffler, , ‘Greed and Grievance in Civil War’. World Bank Policy Research Working Paper, No. 2355Google Scholar.

⁸² The exact definition is a country with territory holding at least 10,000 people and separated from the land area containing the capital city either by land or by 100 kilometres of water. These were coded as ‘non-contiguous’ (see Fearon and Laitin, ‘Ethnicity, Insurgency, and Civil War’).

⁸³ I also include a measure of democracy based on the Polity IV index, which ranges from +10, most democratic, to −10, least democratic (Democracy). All these variables are taken from Fearon and Laitin. I thank them for their generous sharing of data (see Fearon and Laitin, ‘Ethnicity, Insurgency, and Civil War’).

⁸⁴ Coefficients on each of the single-dimension characteristics were also statistically insignificant, as were various combinations of pairs of these variables. For lack of space, these results are not displayed.

⁸⁵ In addition, I ran models using all the other indices of civil war used in this article and all other social structure variables. The conclusion is that F&L’s results on Oil and Income are not robust.

⁸⁶ I note that I also find mixed results for ethnic and religious bipolarization measures, for which Montalvo and Reynal-Querol show strong empirical support (see Montalvo and Reynal-Querol, ‘Ethnic Polarization, Potential Conflict, and Civil Wars’).

⁸⁷ Kam, Cindy D. and Franzese, Robert J., Modeling and Interpreting Interactive Hypotheses in Regression Analysis (Ann Arbor: University of Michigan, 2007)Google Scholar.

⁸⁸ All excluded figures will be made available on the author’s website.

⁸⁹ Full results are available on the author’s website at http://www.umich.edu/~jselway.

⁹⁰ Sarkees, Meredith Reid, ‘The Correlates of War Data on War: An Update to 1997’, Conflict Management and Peace Science, 18 (2000), 123–144CrossRefGoogle Scholar.

⁹¹ See http://globalpolicy.gmu.edu/pitf/

⁹² Marshall, Monty G., ‘Conflict Trends in Africa, 1946–2004: A Macro-Comparative Perspective’, (Arlington, Virginia: Center for Systemic Peace, 2005)Google Scholar.

⁹³ Fearon and Laitin, ‘Ethnicity, Insurgency, and Civil War’.

⁹⁴ For a more in-depth discussion on the important differences amongst these different datasets, see Sambanis, Nicholas, ‘What Is Civil War? Conceptual and Empirical Complexities of an Operational Definition’, Journal of Conflict Resolution, 48 (2004), 814–858CrossRefGoogle Scholar. These additional data are perhaps best seen as additional robustness tests.

⁹⁵ Sambanis, Nicholas, ‘Do Ethnic and Nonethnic Civil Wars Have the Same Causes? A Theoretical and Empirical Inquiry (Part 1)’, Journal of Conflict Resolution, 45 (2001), 259–282CrossRefGoogle Scholar.

⁹⁶ All results are available in the appendix at http://www.umich.edu/~jselway.

⁹⁷ Indeed, the author is currently compiling such data. A more comprehensive project to map the geographic location of ethnic groups is currently being directed by Lars-Erik Cederman and various co-authors. See: Cederman, Rød and Weidmann, ‘Geo-Referencing of Ethnic Groups’.