In the comments, FredR writes:

In [Tolstoy's] Hadji Murad, Chechens come across as border people with a hell of a lot of asabiya.

"Asabiya" is medieval Muslim sociologist Ibn Khaldun's Arabic term for tribal solidarity. You don't want enemies with a lot of asabiya in your country. They go down fighting like these two Chechen terrorists in Boston.

From Wikipedia:

In the August 1996 Battle of Grozny (also known as "Operation Jihad") Chechen rebels regained and then kept control of Chechnya's capital Grozny in a surprise raid.[2] The Russian Federation had conquered the city during the Battle of Grozny (1994–1995) and posted there a large garrison of federal and republican Ministry of the Interior (MVD) troops, but a much smaller rebel force managed to infiltrate Grozny and then either rout or split the MVD forces there into dozens of small pockets of resistance, and over the next five days to beat back and decimate several Russian Ground Forces units that were sent to eject them from the city,[3] resulting in the final ceasefire of the First Chechen War and effectively ending the 1994-1996 conflict.

Okay, the Russian Army usually wins in the end. But, even beating the Russian Army once is impressive.