Steven Pinker calls attention to a new paper:

Are Muslim Countries More War-Prone? Gleditsch, Nils Petter & Ida Rudolfsen (2015) Are Muslim Countries More War-Prone?, Conflict Trends, 3. Oslo: PRIO. In recent years, most civil wars have taken place in Muslim countries. Are Muslim countries more war-prone? Not necessarily, if we look at data for the whole period after World War II. But in the post-Cold War era, most wars are civil wars. Muslim countries have a disproportionate share of these – not because such conflicts have increased, but mainly because other conflicts have declined. This policy brief lists several hypotheses for why this pattern has emerged.

A hypothesis of mine would be that the Fertile Crescent has the oldest civilizations because that’s where agriculture was invented. Thus it has the most ethnic layers (e.g., Alawites, Druze, and Yezidis to name some involved in recent civil wars) due to historical accretion. And thus it has the most complex civil wars of all-against-all, such as in Lebanon, Iraq, and Syria.

To a Middle Easterner, the history of the American Civil War, for example, must seem suspiciously simplistic and puerile: Why are there only two sides fighting? Why is nobody getting holes drilled in his head by neighboring clans?