Have Chechen groups launched terror attacks before?
The Chechens have claimed responsibility for a number of major terror attacks on Russia in the past 10 years, including a 2004 attack on a Russian school in which more than 350 people, many of them children, were killed.
In addition to bombing shopping plazas, apartment buildings, parades, and trains over the years, Chechens launched an attack on a theater in Moscow in 2002 in which they held more than 700 audience members hostage. Russian forces used gas to try and sedate the Chechens, but ended up killing many of the hostages and militants.
Many of the Chechen terrorists involved were women whose militant husbands had been killed by Russian forces, earning them the moniker Black Widows.
The Black Widows became known as a deadly part of the Chechen terror groups, willing to sacrifice themselves as suicide bombers for the Chechen cause.
In 2010, Chechen militants claimed responsibility for the bombing of two metro stations in Moscow, killing nearly 40 people.
What does Dagestan have to do with this?
Dagestan is also a region on the Russian border, part of North Caucasus, and shared a border with Chechnya. Though Dagestan did not fight against Russia for independence after the fall of the Soviet Union, it became known as a lawless and corrupt state. Eventually, Chechen militants began to gain a foothold in Dagestan.
Dagestan has replaced Chechnya as the most volatile region in Russia, with reports of bombings, shootings, and kidnappings occurring every few days.