MOSCOW — – Russia is facing the most serious challenge to its authority in the North Caucasus region since its ill-fated 1994-6 bid to crush rebel guerrillas in Chechnya.
Moscow has sent troops to Dagestan, which borders Chechnya, to combat Chechen-backed fighters who have vowed to drive Russia from the region and to build an Islamic state.
Here is a brief history of Russia's involvement in the North Caucasus region, which neighbors the oil-rich Caspian Sea and the former Soviet republics of Azerbaijan and Georgia.
1722 - Peter the Great annexes Caspian Sea regions of Dagestan at start of a 150-year military campaign to absorb North Caucasus region into Russian Empire.
Mid-19th century - Legendary Imam Shamil uses Islam to weld mountain tribes of Dagestan and Chechnya into formidable fighting force. His ambition is to create a theocratic, Islamic state but he is eventually defeated by Russia's superior numbers and technology.
1917 - Russian revolution brings Communists to power but Islam and traditional clan system remain strong in North Caucasus despite persecution from atheistic Moscow regime.
1944 - Soviet dictator Josef Stalin deports entire Chechen people and their neighbors the Ingush to Central Asia for "collaboration" with German Nazi troops. Tens of thousands die.
1957 - Soviet leader Nikita Khrushchev allows the Chechens back to the Caucasus, setting up the Checheno-Ingush republic.
Oct 1991 - Following the overthrow of local communist ruler Doku Zavgayev, Soviet air force general Dzhokhar Dudayev wins a disputed local poll and declares Chechnya independent.
Russia rejects any talk of independence but takes no action against Dudayev and allows him to run Chechnya.
Dec 1994 - President Boris Yeltsin sends troops to Chechnya to crush the independence movement. Tens of thousands, mostly civilians, die in ensuing 20-month war. The capital, Grozny, is reduced to rubble. Rebels are driven to the mountains but are not defeated.
Aug 1996 - Rebels seize Grozny. Moscow signs a truce on August 31 providing for a Russian pullout and deferring issue of Chechen independence for five years.
Jan 1997 - Former rebel chief of staff, Aslan Maskhadov, a relative moderate, wins Chechen presidential election with almost 65 percent of vote. Last Russian troops leave Chechnya.
Jan 1997 - Unidentified kidnappers seize two Russian journalists in Chechnya, first in a long series of abductions for ransom money which fuel tensions with Moscow and effectively block the reconstruction of the shattered economy.
May 12 1997 - Yeltsin and Maskhadov sign peace accord but Chechnya's final status still unresolved. Moscow says Chechnya must stay part of Russian Federation, albeit with wide autonomy.
September 1998 - Chechen warlords demand the resignation of President Maskhadov, saying he is too conciliatory towards Moscow. Maskhadov also under pressure from Russia, which says he is failing to combat organized criminal gangs whose frequent kidnappings have turned Chechnya into no-go zone for outsiders.
July 1999 - Russian troops clash increasingly fiercely with Chechen fighters near Chechnya's border with Dagestan.
Aug 7 1999 - Russian helicopters pound positions held by Islamic militants in Dagestan said to have come from Chechnya. Moscow vows firm action to dislodge intruders.
Aug 8 - Russian Prime Minister Sergei Stepashin visits Dagestan to discuss crisis with local commanders and officials.
Aug 9 - Yeltsin sacks Stepashin and nominates security chief Vladimir Putin as Russian prime minister. Stepashin says Russia could lose Dagestan just as it lost Chechnya.
Aug 10 - Islamic fighters declare Dagestan an independent state and call for holy war of liberation against Moscow rule.
Aug 11 - Feared Chechen warlord Shamil Basayev declares he is behind Dagestan rebellion and vows to drive Russian "infidels" from whole North Caucasus region. Russian officials say 10 federal troops have died and 27 more wounded so far.
Aug 12 - President Yeltsin says he is confident of victory over the rebels. Warplanes and artillery continue to pound the rebels' positions as more men and supplies arrive in Dagestan
Aug 13 - Russian Acting Prime Minister Vladimir Putin says an assault has begun to drive the rebels out of their mountain strongholds and that they would be hit everywhere, even in bases in Chechnya.
Aug 14 - Russia says at least 200 guerrillas have been killed in the fighting and puts Russian losses at 14.
The rebels, via a site on the Internet, say they have killed 130 Russian soldiers and officers, destroyed nine helicopters and shot down one fighter jet.
Aug 15 - Chechnya declares month-long state of emergency, from August 16 to September 16, including a curfew and ban on all media expect state television, saying it must be ready for acts of provocation by Russia.