Two young men—brothers Dzhokhar A. Tsarnaev and Tamerlan Tsarnaev with origins in Russia’s volatile North Caucasus regions—have been connected to this week’s bomb attacks at the Boston Marathon. They lived, for a time, in Dagestan, which is recognized as the epicenter of the Islamic insurgency that spilled over from Chechnya. Senior Fellow Fiona Hill, director of the Center on the United States and Europe, says Chechnya and Russia have spent centuries at war and it isn’t surprising that this conflict, which has spanned generations, would provide fertile ground to incite and radicalize sympathizers wherever they happen to live.
The US has flaked out on the Kurds in the past, so it's understandable that they're worried about US withdrawal in Syria now, but in this case, the US won't be going anywhere for a while. Once ISIL is defeated, the US will need proxy forces on the ground to push back against both Assad and Russia.