An influential conventional wisdom holds that civil wars proliferated rapidly with the end of the Cold War and that the rootcause of many or most of these has been ethnic nationalism.
We show that the current prevalence of internal war is mainly the result of a steady accumulation of protracted conflicts since the 50s and 60s rather than a sudden change associated with a new, post-Cold War international system. We also find that after controlling for per capita incomes and growth rates, more ethnically or religiously diverse countries have been no more likely to experience significant civil war in this period. We argue for understanding civil war in this period in terms of insurgency or rural guerrilla warfare, a particular form of military practice that can be harnessed to diverse political agendas, including but not limited to ethnic nationalism.
The factors that explain which countries have been at risk for civil war are not their ethnic or religious characteristics but rather the conditions that favor insurgency. These include poverty and slow growth, which favor rebel recruitment and mark financially and bureaucratically weak states, rough terrain, and large populations.
–James D. Fearon and David D. Laitin: Ethnicity, Insurgency, and Civil War (PDF, Stanford University, 20. August 2001)