Russia’s volatile North Caucasus, which the two suspects in the Boston Marathon bombings once called home, have seen two decades of brutal fighting between Russian forces and separatists bent on carving out an independent Islamic state.

There was no information on any possible links between the suspects and any insurgent group. Tamerlan Tsarnaev — the 26-year-old killed in a gun battle with police in Massachusetts overnight — and his 19-year-old brother Dzhokhar are ethnic Chechens whose family left Chechnya long ago and moved to Central Asia, according to the Chechen government.

Before moving to the United States a decade ago, their uncle said, the brothers lived briefly in Makhachkala, the capital of Dagestan. Their father lives there now.

The conflict in Chechnya began in 1994 as a separatist war, but quickly morphed into an Islamic insurgency dedicated to forming an Islamic state in the Caucasus. Dagestan has since become the epicenter of the insurgency.

Russian troops withdrew from Chechnya in 1996 after the first Chechen war, leaving it de-facto independent and largely lawless, but then rolled back three years later following apartment building explosions in Moscow and other cities blamed on the rebels.

Russia faced strong international criticism for its indiscriminate use of force against civilians and other rights abuses in Chechnya. The two separatist wars killed an estimated 100,000 people, and Russian bombing reduced most of Chechnya’s capital, Grozny, and many other towns and villages to rubble, sending tens of thousands fleeing.

Chechnya has stabilized under the steely grip of Kremlin-backed local strongman Ramzan Kadyrov, a former rebel whose forces have been accused of severe human rights abuses. But the Islamic insurgency has spread to neighboring provinces, with Dagestan — sandwiched between Chechnya and the Caspian Sea — becoming the epicenter of violence. Militants launch daily attacks against police and other authorities.

Militants from Chechnya and neighboring provinces have carried out a long series of terrorist attacks in Russia, including a 2002 raid of a Moscow theater, in which 129 hostages died; a 2004 hostage-taking at a school in the southern city of Beslan that killed more than 330 people, and numerous bombings in Moscow and other cities.

The Obama administration placed Chechen warlord Doku Umarov on a list of terrorist leaders after he claimed responsibility for March 2010 suicide bombings on Moscow’s subway that killed 40 people and a November 2009 train bombing that claimed 26 lives.

In recent years, however, militants in Chechnya, Dagestan and neighboring provinces have largely refrained from attacks outside the Caucasus.

Russian officials and experts have claimed that rebels in Chechnya had close links with al-Qaida. They say dozens of fighters from Arab countries trickled into Chechnya during the fighting there, while some Chechen militants have gone to fight in Afghanistan.

The U.S. has long urged Russia’s government and separatist elements in Chechnya not aligned with al-Qaida or other terrorist organizations to seek a political settlement.

Washington provided aid to the area during the high points of fighting in the 1990s and in the early 2000s, and has demanded human rights accountability. But the U.S. always backed the territorial integrity of Russia, never endorsing the separatists’ desire for an independent state. And it has supported Russia’s right to root out terrorism in the region.

Dozens of Chechens have trained in Pakistan’s northwest frontier of Waziristan, but most have returned to Russia to fight.

Recently, however, the al-Qaida inspired group Tehrik-e-Taliban Pakistan has made strides at recruiting European fighters for attacks against the West, according to Noman Benotman, a former jihadist fighter who now works for the London-based Quillium Foundation.

The TTP, which has supported attacks in response to U.S. drone strikes, was linked to the failed 2010 attack in New York City’s Times Square.

“I would be surprised if these attacks were the work of lone wolves,” Benotman said.

In recent years, people from Chechnya have faced charges in several European countries.

In 2011, a Danish court sentenced a Chechen-born man to 12 years in prison for preparing a letter bomb that exploded as he was assembling it in a Copenhagen hotel.

Last month, Spain’s Interior Ministry said French and Spanish police arrested three suspected Islamic extremists in an operation in and around Paris. A statement said the suspected activists were of Chechen origin and believed linked to a terror cell dismantled last August in southern Spain.

Last August, a Turk and two Russians of Chechen descent were arrested and jailed in Spain on charges of belonging to an unnamed terror organization and possession of explosives. They have since been released while investigations continue.