The Cold War officially ended in 1991, following the dissolution of the Soviet Union. Tensions between the United States and the Soviet Union, which had dominated global politics since the end of World War II, began to wane throughout the late 1980s, marked by a series of reforms by Soviet leader Mikhail Gorbachev, such as Glasnost (openness) and Perestroika (restructuring). The fall of the Berlin Wall in 1989 symbolized the collapse of communist regimes in Eastern Europe. As the Soviet Union disintegrated in December 1991, it marked the definitive conclusion of the ideological and geopolitical rivalry that characterized the Cold War.