The New York Times Sunday magazine included this interesting article by Gary J. Bass, who writes:
The commonplace assumption that a more homogeneous society is a more peaceful society certainly sounds reasonable. Surely monoethnic Japan should have an easier time maintaining domestic order than Indonesia; or Slovenia than Macedonia.
After all, in a country with numerous ethnic or religious groups, politicians are easily tempted to organize factions along group lines ...
But what if this whole premise is wrong? Odd as it may seem, there is a growing body of work that suggests that multiethnic countries are actually no more prone to civil war than other countries.
In a sweeping 2003 study, the Stanford civil war experts James D. Fearon and David D. Laitin came to a startling finding: “it appears not to be true that a greater degree of ethnic or religious diversity — or indeed any particular cultural demography — by itself makes a country more prone to civil war.”
Fearon and Laitin looked at 127 civil wars from 1945 to 1999, most often in sub-Saharan Africa and Asia. They found that regardless of how ethnically mixed a country is, the likelihood of a civil war decreases as countries get richer. The richest states are almost impervious to civil strife, no matter how multiethnic they might be — think for instance of Belgium, where Flemings and Walloons show almost no inclination to fight it out.