The attack by Tamerlan and Dzhokhar Tsarnaev has invariably elicited comparisons to the Saudi-born terrorists who struck the United States on September 11, 2001, or to the Pakistani immigrant Faisal Shahzad, who attempted to set off a car bomb in Times Square in 2010. Others have suggested that the 26-year-old Tamerlan, an ethnic Chechen, may have witnessed the Russian/Chechen war of 1999, or Russia’s brutal efforts to pacify insurgent fighting in the North Caucasus.