Islamic militants emerged as the most likely suspects behind the Moscow airport attack. There has been no claim of responsibility but early witness reports suggested the bomber had a "North Caucasus appearance".
Russia fought two wars to regain hold of Chechnya in the late 1990s and early 2000s, and the region has been rebuilt and is run by the Kremlin-friendly former fighter Ramzan Kadyrov. But in Chechnya, and even more so in neighbouring Ingushetia and Dagestan, elements of an insurgency remain.
They are nominally led by Doku Umarov, self-styled "Emir of the Caucasus", who says he wants to create an Islamic caliphate across the Caucasus.
Nobody knows exactly how many people are actively involved in the insurgency.
Terrorist attacks in the North Caucasus on police and security forces are frequent. Almost daily in Dagestan and Ingushetia, there are reports of policemen killed, traffic police shot at, or shootouts between security forces and militants. The battle against the insurgency in the North Caucasus is a low-grade war that rarely features on the news bulletins of state-controlled television.
Attacks on civilians, and attacks in Russia proper, are much rarer, but when they do come, they remind people in Moscow of the ongoing instability in the south of the country.
President Dmitry Medvedev has already vowed to catch those responsible for yesterday's attack, and there may well be increased military operations in the North Caucasus. Security measures will doubtless be increased at airports and other infrastructure installations. But the North Caucasus is, after all, part of Russia, and it's doubtful whether even the most stringent security could prevent determined suicide bombers.
For that, they will need to end sympathy for the insurgency in the Caucasus, whether by force or by persuasion, a goal which seems more elusive with every terrorist atrocity. In 1999, Vladimir Putin, who had been recently made prime minister by Boris Yeltsin, famously promised to "waste" terrorists in the "outhouse". More than 11 years later, the terrorists have shown again that they can strike at the very heart of Russia. (© Independent News Service)