<P> Latvia declared the restoration of independence on May 4, 1990, with the declaration stipulating a transitional period to complete independence . The Declaration stated that although Latvia had de facto lost its independence in World War II, the country had de jure remained a sovereign country because the annexation had been unconstitutional and against the will of the Latvian people . The declaration also stated that Latvia would base its relationship with the Soviet Union on the basis of the Latvian--Soviet Peace Treaty of 1920, in which the Soviet Union recognized Latvia's independence as inviolable "for all future time". May 4 is now a national holiday in Latvia . </P> <P> On May 7, 1990, Ivars Godmanis of the Latvian Popular Front was elected chairman of the Council of Ministers (the equivalent of being Latvia's Prime Minister). </P> <P> During the first week of January 1990, in the Azerbaijani exclave of Nakhchivan, the Popular Front led crowds in the storming and destruction of the frontier fences and watchtowers along the border with Iran, and thousands of Soviet Azerbaijanis crossed the border to meet their ethnic cousins in Iranian Azerbaijan . It was the first time the Soviet Union had lost control of an external border . </P> <P> Ethnic tensions had escalated between the Armenians and Azerbaijanis in spring and summer 1988 . On January 9, 1990, after the Armenian parliament voted to include Nagorno - Karabakh within its budget, renewed fighting broke out, hostages were taken, and four Soviet soldiers were killed . On January 11, Popular Front radicals stormed party buildings and effectively overthrew the communist powers in the southern town of Lenkoran . Gorbachev resolved to regain control of Azerbaijan; the events that ensued are known as "Black January ." Late on January 19, 1990, after blowing up the central television station and cutting the phone and radio lines, 26,000 Soviet troops entered the Azerbaijani capital Baku, smashing barricades, attacking protesters, and firing into crowds . On that night and during subsequent confrontations (which lasted until February), more than 130 people died . Most of these were civilians . More than 700 civilians were wounded, hundreds were detained, but only a few were actually tried for alleged criminal offenses . </P>

What caused the breakdown of the soviet union