The Caucasus region of Eurasia, wedged in between the Black and Caspian Seas, encompasses the modern territories of Armenia, Azerbaijan, and Georgia, as well as the troubled republic of Chechnya in southern Russia. A site of invasion, conquest, and resistance since the onset of historical record, it has earned a reputation for fearsome violence and isolated mountain redoubts closed to outsiders. Over extended efforts to control the Caucasus area,...