With Soviet encouragement, Mongolia increased its participation in communist-sponsored conferences and international organizations. In 1955, Mongolia attempted to join the United Nations, but the request was vetoed by the Republic of China (now based on Taiwan) which maintained their renewed claim over Mongolia. Mongolia became a member of the UN in 1961 after the Soviet Union threatened to veto the admission of all of the newly decolonized states of Africa if the Republic of China again used its veto. Diplomatic relations with the United States were not established until near the end of the Cold War. Mongolia became a bone of contention between the Soviet Union and China following the Sino-Soviet split because of the presence of Soviet nuclear arms.