Migrants from the republics of the north Caucasus and the post-Soviet countries of Central Asia have also spread more conservative interpretations of Islam.

ECONOMIST: Russia and Islam

Scott Gehlbach and Konstantin Sonin, of the Centre for Economic and Financial Research in Moscow, argue that three factors have influenced businessmen to go into politics in post-Soviet countries.

ECONOMIST: Why do professional paths to the top vary so much?

But few of these post-Soviet countries have been as valuable, pound-for-pound, to the United States in the last 20 years as Azerbaijan, a country that we all should seek to understand due to the resilience of its economy, richness of its culture and the relevance of its policies.

FORBES: America, Meet Azerbaijan

Regional tensions have been further exacerbated by the different ways the various Central Asian countries have dealt with the post-Soviet transition.

ECONOMIST: The heavy costs of non-co-operation