The historical event that marked the collapse of the Soviet Union in 1991 was the official dissolution of the USSR on December 26, 1991. This event followed a series of political changes and economic turmoil in the late 1980s, influenced by Mikhail Gorbachev's policies of glasnost (openness) and perestroika (restructuring). These reforms aimed to modernize the stagnating Soviet economy but inadvertently weakened central control. Various republics within the union declared independence, leading to a fragmented political landscape. The end of the Soviet Union not only transformed Eastern Europe but also had global implications, ending the Cold War and reshaping international relations.