While nothing has yet been found linking brothers Tamerlan Tsarnaev, 26, who was killed by authorities, and 19-year-old Dzhokhar Tsarnaev to Chechen terrorist organizations, their ethnicity has once again directed attention to Russia's Caucasus region. (Read "Chechnya: How did it come to this?" in National Geographic magazine.)

The area occupies Russia's underbelly, situated between the Caspian and Black Seas, and has been a cauldron of ethnic and nationalist discontent for centuries.

First subdued by the tsars in the 19th century, the Caucasus are a patchwork of peoples, languages, and cultures that have always stood distinct from their Russian rulers.

From Georgians in the west to Azeris in the south to Chechens, Dagestanis, and Circassians in the north, the region is riven with