Republic asked to join the Warsaw Pact under Article 9 of the treaty. Due to the emerging Sino-Soviet split, Mongolia remained in an observer status. In what was the first instance of a Soviet initiative being blocked by a non-Soviet member of the Warsaw Pact, Romania blocked Mongolia's accession to the Warsaw Pact. The Soviet government agreed to station troops in Mongolia in 1966. At first, China, North Korea, and North Vietnam had observer status, but China withdrew in 1961 as a consequence of the Albanian-Soviet split, in which China backed Albania against the USSR as part of the larger Sino-Soviet split of the early 1960s. During the Cold War For 36 years, NATO and the Warsaw Pact never directly waged war against each other in Europe; the United States and the Soviet Union and their respective allies implemented strategic policies aimed at the containment of each other in Europe, while working and fighting for influence within the wider Cold War on the international stage. These included the Korean War, Vietnam War, Bay of Pigs invasion, Dirty War, Cambodian–Vietnamese War, and others. In 1956, following the declaration of the Imre Nagy government of the withdrawal of Hungary from the Warsaw Pact, Soviet troops entered the country and removed the government. Soviet forces crushed the nationwide revolt, leading to the death of an estimated 2,500 Hungarian citizens. The multi-national Communist armed forces' sole joint action was the Warsaw Pact invasion of Czechoslovakia, another Warsaw Pact member state, in August 1968. All member countries, with the exception of the Socialist Republic of Romania and the People's Republic of Albania, participated in the invasion. The German Democratic Republic provided only minimal support. End of the Cold War In 1989, popular civil and political public discontent toppled the Communist governments of the Warsaw Treaty countries. The beginning of the end of the Warsaw Pact, regardless of military power, was the Pan-European Picnic in August 1989. The event, which goes back to an idea by Otto von Habsburg, caused the mass exodus of GDR citizens and the media-informed population of Eastern Europe felt the loss of power of their rulers and the Iron Curtain broke down completely. Though Poland's new Solidarity government under Lech Wałęsa initially assured the Soviets that it would remain in the Pact, this broke the brackets of Eastern Europe, which could no longer be held together militarily by the Warsaw Pact.