Anyone following events in Iraq could be forgiven for thinking that we know relatively little about the dynamics of communal civil wars. In addition, anyone who remembers Bosnia and the rest of the “ugly nineties” has observed that the list of countries that have ripped themselves apart in communal civil wars seems to be growing. At the same time, resolving these conflicts is now seen as a deeply intractable problem. In almost every region we observe, communal civil wars are at or near the top of US policy agendas, most of all in Iraq, but also in the Israeli-Palestinian conflict and Darfur.

In fact, we have learned quite a lot about civil wars. Before the conflict in Bosnia, the conventional wisdom was that multi-communal states that had been torn apart by war should be put back together by power-sharing between communities or electoral reform. Such initiatives, it was reasoned, would compel politicians to appeal to all communities, not just their own, as well as to third party aid for reconstruction. Unfortunately, these approaches have rarely worked well.

Bosnia and subsequent conflicts demonstrate that communal settlement pat terns matter a great deal. While earlier theories of communal conflict focused on factors such as the legitimacy of the state, histories of communal compromise and confrontation, and the intensity of communal grievances (whether real or exaggerated by hypernationalist mythmakers), the conflict in Bosnia allowed the international community to develop a new theory centered on security dilemmas.

Whenever centrally imposed order in any communally divided state collapses, as in the case of the Soviet Union and Yugoslavia, or when the United States destroyed Saddam Hussein’s regime in Iraq, communities must rely on their own resources for self-defense. In effect, the communally divided state becomes a pocket international system, and behaves like one.

The problem is that the material measures—and even the rhetorical measures—that communities use to mobilize for defense also pose offensive threats to other communities. The result is a security dilemma: a situation in which no community can provide for its own security without threatening the security of others. If and when this reaches the point that all sides are mobilized for war, or if large-scale violence has already commenced, it ceases to matter whether the original reasons for conflict were based on real material interests or were whipped up by political elites using populist rhetoric for their personal gain. Nor does it matter which side started the spiral into internal conflict: each group’s mobilization now poses a real security threat to other groups.

The Case of Bosnia: A Security Dilemma

Of course, the nature and intensity of this mutual security dilemma can vary, depending in large part on communal settlement patterns. The more intermixed the settlement pattern of the hostile populations, the greater the offensive opportunities for each side—not only for organized forces but also for bandits and terrorists. Each group is likely to feel compelled to eliminate enclaves of the other community settled in their midst, lest these form fifth columns or become targets of “rescue offensives,” as in the case of the Israeli offensive of 1948. In that mission, the Israeli government incorporated the isolated Jewish enclave of West Jerusalem into Israel by overrunning the Arab towns between Tel Aviv and Jerusalem.

The worst dangers are posed by people who are settled in places that make them appear both vulnerable and threatening to the other side at the same time. People in this situation are the ones most likely to become victims of ethnic cleansing. The heaviest fighting and worst atrocities in Bosnia happened in places where Serb and Muslim populations were most heavily intermixed, in the Drina Valley in Eastern Bosnia and in the North Central “Posavina Corridor,” where Muslims lived not only with Serbs but also astride the only possible route that could connect the two main Serb enclaves in Bosnia.

The map of Bosnia below does not fully capture the degree to which settlements were intermixed in the Drina Valley, where towns were mostly Muslim and the rural population nearly all Serb. The January 1995 map does not show all of the important places where ethnic cleansing took place; of the four isolated green spots in Eastern Bosnia, two were overrun by Serb forces who committed terrible atrocities there, one was captured by a Muslim “rescue offensive,” and the fourth was awarded to the Muslims in the Dayton Agreement.

Communal violence also hardens identities. The fact that before the war, many Bosnians thought of themselves as Yugoslavs before Serbs or Muslims did not help curb the violence. For during an ethnic war, communal identity is not a matter of choice; it is enforced by armed members of the enemy community who do not stop to ask their victims about their moderate or cosmopolitan sympathies.

The same phenomenon has happened in Iraq since 2003. While before 2003 many people considered their Iraqi or Arab identities more important than any sectarian affiliation, the war and its murderous death squads have forced Iraqi citizens to adopt their narrower identities of Sunni, Kurd, or Shia.

Wars also generate memories of atrocities that cannot be erased, giving ultranationalists within each community a political advantage even years after the war has ended. This renders solutions that require some degree of inter-communal trust, such as power-sharing, virtually impossible to implement during a war, or for a long time afterward.

Although the human suffering in Bosnia horrified the world, it took three and a half years to devise a viable solution. This was not because Western officials were inexperienced or uncaring, but because it took them this long to understand that pre-Bosnia prescriptions, such as state-building and power-sharing, would not work. Peace, for Bosnia, required engaging seriously with the logic of communal war itself—especially the issue of ethnic geography and the hardening of identities. This meant accepting a very loose federal arrangement, which amounted to de facto partition.

By the time of Dayton in November 1995, the expulsion or flight of refugees had left only about 150,000 people living in areas controlled by a different community. Even after Dayton, further communal segregation continued for several years, although the trend is now beginning to be reversed.