Feb. 28-29, 1988: After two weeks of Armenian demonstrations demanding that the largely Armenian enclave of Nagorno-Karabakh, in Azerbaijan, be ceded to Armenia, ancient tensions between predominantly Christian Armenians and primarily Muslim Azerbaijanis explode in the Azerbaijan city of Sumgait. At least 32 people, mostly Armenians, are killed.

Mar. 1, 1988: The Soviet authorities announce that military forces were called in to quell the clashes in Sumgait, said to be the most serious outbreak of nationalist unrest in the Soviet Union since the early 1920's.

May 21, 1988: The Communist Party leaders of Armenia and Azerbaijan are dismissed after huge street demonstrations in the Armenian capital, Yerevan, and the Azerbaijan capital, Baku, and newed violence.

July 4-5, 1988: Armenian nationalist demonstrators close the main airport of Yerevan; there are widespread strikes in Yerevan and Nagorno-Karabakh.

July 18, 1988: The Soviet Government rejects a decision by Nagorno-Karabakh to break away from the republic of Azerbaijan.

Sep. 21-22, 1988: After several days of ethnic turmoil in Nagorno-Karabakh, Moscow declares a state of emergency in the disputed southern territory. Soviet troops are deployed around Government buildings in Armenia; Armenians hold mass demonstrations and strike.

Nov. 24-25, 1988: The Soviet military takes control of Baku and Yerevan after several days of new clashes, in which three soldiers are killed and 126 people wounded. . Officials say that 100,000 refugees have fled their homes in the two republics and at least 28 people are killed in the new wave of rioting.

Dec. 7, 1988: A devastating earthquake strikes Armenia, leaving at least 25,000 dead, according to conservative Soviet Government estimates.

Jan. 12, 1989: The Soviet Government decides to put Nagorno-Karabakh under direct rule from Moscow.

June 4, 1989: Increased tension and street demonstrations in Nagorno-Karabakh coincide with a heated debate on the issue in the new Congress of People's Deputies; a month-long general strike paralyzes Nagorno-Karabakh's capital, Stepanakert.

Aug. 29, 1989: Soviet troop reinforcements are sent to Nagorno-Karabakh after new fighting between Armenians and Azerbaijanis.

Sep. 25, 1989: President Gorbachev calls on Azerbaijani and Armenian leaders to negotiate an end to a rail blockade, which has for over a month blocked supplies for earthquake reconstruction, caused fuel shortages and threatens food supplies. Azerbaijani railworkers began their blockade during a strike by nationalists to press their claims to Nagorno-Karabakh.

Nov. 28, 1989: The Supreme Soviet restores Azerbaijan's control over Nagorno-Karabakh, abolishing the special national committee that had been running the embattled region since the beginning of the year.

Dec. 1, 1989: After Armenians hold new rallies, the Armenian Parliament condemns Moscow's decision to restore Azerbaijan's control over the territory and votes to unite with Nagorno-Karabakh. In response, the nationalist Azerbaijani Popular Front reimposes the rail blockade against Armenia.

Jan. 14, 1990: Over the weekend, Azerbaijan erupts in civil violence. At least 25 people are killed in Baku, and several towns are left in disarray.

Jan. 15: The Soviet Union issues a sweeping emergency decree declaring a state of emergency in parts of Azerbaijan and ordering army, navy and K.G.B. security forces to help contain fighting that the Soviet press portrays as verging on civil war.

Jan. 16: The Soviet Government airlifts 11,000 army and internal police troops to the embattled regions of Azerbaijan, where armed bands of Armenian and Azerbaijani are still fighting. The Government puts the death toll at 56 in several days of bloodshed, with most of the victims being Armenians killed by mobs in Baku.

Jan. 17: Soviet troops try to impose martial law in Azerbaijan but are hampered by roadblocks in the hilly countryside.

Jan. 18: Soviet troops seeking to end the violence in Azerbaijan, continue to be bogged down by widespread obstruction, including air and rail blockades, sabotage, hostage-taking and civil disobedience.

Jan. 19: In Baku, Soviet troops fire on Azerbaijanis and push through barricades with tanks, continuing their efforts to end the civil insurrection.