From PLOS One (via HBD Chick):

Alex Rutherford, Dion Harmon, Justin Werfel, Alexander S. Gard-Murray, Shlomiya Bar-Yam, Andreas Gros, Ramon Xulvi-Brunet, Yaneer Bar-Yam mail Published: May 21, 2014

Abstract

We consider the conditions of peace and violence among ethnic groups, testing a theory designed to predict the locations of violence and interventions that can promote peace. Characterizing the model's success in predicting peace requires examples where peace prevails despite diversity. Switzerland is recognized as a country of peace, stability and prosperity. This is surprising because of its linguistic and religious diversity that in other parts of the world lead to conflict and violence. Here we analyze how peaceful stability is maintained. Our analysis shows that peace does not depend on integrated coexistence, but rather on well defined topographical and political boundaries separating groups, allowing for partial autonomy within a single country. In Switzerland, mountains and lakes are an important part of the boundaries between sharply defined linguistic areas.

Political canton and circle (sub-canton) boundaries often separate religious groups. Where such boundaries do not appear to be sufficient, we find that specific aspects of the population distribution guarantee either sufficient separation or sufficient mixing to inhibit intergroup violence according to the quantitative theory of conflict. In exactly one region, a porous mountain range does not adequately separate linguistic groups and that region has experienced significant violent conflict, leading to the recent creation of the canton of Jura. Our analysis supports the hypothesis that violence between groups can be inhibited by physical and political boundaries. A similar analysis of the area of the former Yugoslavia shows that during widespread ethnic violence existing political boundaries did not coincide with the boundaries of distinct groups, but peace prevailed in specific areas where they did coincide. The success of peace in Switzerland may serve as a model to resolve conflict in other ethnically diverse countries and regions of the world.

Switzerland, unlike, say, most of sub-Saharan Africa, has a lot of topography. Mountain ranges tend to reduce intercourse between the two sides, and lakes make better political borders than rivers . Moreover, the Swiss tend to be fairly cooperative so the people semi-isolated between a mountain range and a lake, say, get along pretty well with their neighbors. People who don't want to adopt their neighbors language or religion can move a relatively short distance to an area more suitable to their predilections.So, in Switzerland the internal boundaries have largely been worked out by the locals over the centuries, but in Yugoslavia they were imposed by the half-Croat, half-Slovene Tito to keep the Serbs down. Tito's plan worked pretty well for a long time, but eventually led to fighting and ethnic cleansing, such as the expulsion of Serb residents from Croatia in 1995's Operation [Desertless] Storm.

I wrote about Switzerland back in 2000 for VDARE.