The attack was conducted by the "Black Widows," these are widows of North Caucasus fighters who died fighting the Russians. The Black Widows are a prime example of the globalization of the North Caucasus wars. The first war, the First Chechen War, was a nationalist rebellion by ethnic Chechens who wanted independence for their idealized secular republic. After lawlessness took over the government was seized by radicals who embraced Islamism and allowed foreign fighters to enter Chechnya. By the time the second war, the 1999 Dagestan War, erupted, foreign fighters and organizations had radicalized much of Chechen society. During the take over of the Moscow theater in 2002 Black Widows were wearing full burqas and Arabic script was imprinted on their flags. Today radical Chechens have been caught and killed in Iraq, Afghanistan, and Pakistan.
Russia is facing an increasing radical, expansionist insurgency. The nationalist rebellion became an Islamist insurrection. Besides the probable/possible(?) Islamist apartment bombings around Moscow, the terrorism was mostly confined to the North Caucasus. However, attacks have gone from every other year, like the 2002 theater siege and the 2004 Moscow Metro bombing, to monthly. Train bombings are becoming much more common in European Russia and one wonders how common small attacks occur or are attempted.
The War in the North Caucasus and its violent fits elsewhere in Russia will be the conflict to watch as it will show how a "hearts and mind"-free counterinsurgency works (or does not work) and if foreign Islamists attempt to swarm this battlefield as they have in Afghanistan, Iraq, and Somalia.