Check out this map, which is dominated by the Muslim world.
Stanley Kurtz of the Hoover Institution has argued that such intermarriage patterns make liberal democracy harder:
In the modern Middle East, networks of kin are still the foundation of wealth, security, and personal happiness. That, in a sense, is the problem. As we’ve seen in Afghanistan, loyalty to kin and tribe cuts against the authority of the state. And the corrupt dictatorships that rule much of the Muslim Middle East often function themselves more like self-interested kin groups than as rulers who take the interests of the nation as a whole as their own. That, in turn, gives the populace little reason to turn from the proven support of kin and tribe, and trust instead in the state.
An intriguing idea, but I find it very hard to establish the appropriate causal connections. Still, better that we ponder the question than stick our heads in the sand. Parapundit offers a very useful overview of the debate, sympathetic to Kurtz’s point of view. Please note, as always, that use of a link does not constitute endorsement of all of that link’s contents or subsequent links.