Unrest culminated in violent confrontation when Soviet troops killed 132 nationalist demonstrators in Baku on 20 January 1990. Azerbaijan declared independence from the USSR on 30 August 1991 and became part of the Commonwealth of Independent States. The First Nagorno-Karabakh War began by the end of the year, ending in a tense cease-fire which has persisted into the 21st century. The refusal by both sides to negotiate resulted in a stalemate, as Armenian troops retained their positions in Karabakh and corridors to Armenia which were seized from Azerbaijan.