According to the Council on Foreign Relations analysis, a Chechen warlord is said to have met with Osama bin Laden while both were fighting against the Soviet occupation of from 1979-89. Justice Department said in a 2004 report that Zacharias Moussaoui, who was convicted for his role in the 9/11 attacks, had previously sought to recruit at least one man to fight in Chechnya.
Authorities have also found links between Chechen separatists and other Islamist terrorist groups. Intelligence officials in France had warned the FBI of Moussaoui's connection to the Chechen fighters.
Shortly after the Soviet Union's collapse, Chechnya declared independence from Russia, a move that eventually led to war from 1994-1996 when tens of thousands died and Russian regained control of the republic.
The Tsarnaev family reportedly fled Chechnya for nearby Kazakhstan and, later, the United States.
Ruslan Tsarni of Montgomery Village, Md., the uncle of the two brothers, said the family was ethnic Chechen.
Author Kimberly Marten, who researched Chechnya for her recent book, Warlords Strong-Arm Brokers in Weak States, cautioned Friday against concluding that the Boston attack was an act of terror."We shouldn't assume...
They had no escape plan to leave the country," Schanzer said.
Of the region's almost 1.3 million residents, ethnic Chechens make up about 95%, according to Russian government statistics.
Chechen militants have committed sporadic large-scale attacks in Russia since the 1990s.
In March 2010, Chechen terrorists claimed responsibility for bombings on the Moscow subway system that killed more than 40 people.
Fighting broke out in Chechnya again in 2000 when Russian forces destroyed much of the republic's capital city of Grozny in a bid to crush resistance.
With the killing of key militant leaders, the separatist movement has been quelled, although violence in the region continues.