中ソ国境紛争
Under the Brezhnev Doctrine, the Soviet Union reserved the right to intervene in other socialist states. In response, China moved towards the United States following the Sino-Soviet border conflict and later reformed and liberalized its economy while the Eastern Bloc saw the Era of Stagnation in comparison with the capitalist First World. The Soviet–Afghan War nominally expanded the Eastern Bloc, but the war proved unwinnable and too costly for the Soviets, challenged in Eastern Europe by the civil resistance of "Solidarity". In the late 1980s, Soviet leader Mikhail Gorbachev pursued policies of "glasnost" (openness) and "perestroika" (restructuring) to reform the Eastern Bloc and end the Cold War, which brought forth unrest throughout the bloc.