1949
October 1949: People’s Republic of China Established
Chinese Communist Party leader Mao Zedong establishes the People’s Republic of China in Beijing on October 1 after peasant-backed Communists defeat the Nationalist government of Chiang Kai-shek. Chiang and thousands of his troops flee to Taiwan. The United States—which backed the Nationalists against invading Japanese forces during World War II—supports Chiang’s exiled Republic of China government in Taipei, setting the stage for several decades of limited U.S. relations with mainland China.
1950
June 1950: Korean War Breaks Out
The Soviet-backed North Korean People’s Army invades South Korea on June 25. The United Nations and the United States rush to South Korea’s defense. China, in support of the communist North, retaliates when U.S., UN, and South Korean troops approach the Chinese border. As many as four million people die in the three-year conflict until the United Nations, China, and North Korea sign an armistice agreement in 1953 [PDF].
1954
August 1954: First Taiwan Strait Crisis
President Dwight Eisenhower lifts the U.S. navy blockade of Taiwan in 1953, leading Chiang Kai-shek to deploy thousands of troops to the Quemoy and Matsu islands in the Taiwan Strait in August 1954. Mainland China’s People’s Liberation Army responds by shelling the islands. Washington signs a mutual defense treaty with Chiang’s Nationalists. In the spring of 1955, the United States threatens a nuclear attack on China. That April, China agrees to negotiate, claiming a limited victory after the Nationalists' withdrawal from Dachen Island. Crises erupt again in 1956 and 1996.
1959
March 1959: Tibetan Uprising
Nine years after the People’s Republic of China asserts control over Tibet, a widespread uprising occurs in Lhasa. Thousands die in the ensuing crackdown by PRC forces, and the Dalai Lama flees to India. The United States joins the United Nations in condemning Beijing for human rights abuses in Tibet, while the Central Intelligence Agency helps arm the Tibetan resistance beginning in the late 1950s.
1964
October 1964: China’s First Atomic Test
China joins the nuclear club in October 1964 when it conducts its first test of an atomic bomb. The test comes amid U.S.-Sino tensions over the escalating conflict in Vietnam. By the time of the test, China has amassed troops along its border with Vietnam.
1969
March 1969: Sino-Soviet Border Conflict
Differences over security, ideology, and development models strain Sino-Soviet relations. China’s radical industrialization policies, known as the Great Leap Forward, lead the Soviet Union to withdraw advisors in 1960. Disagreements culminate in border skirmishes in March 1969. Moscow replaces Washington as China’s biggest threat, and the Sino-Soviet split contributes to Beijing’s eventual rapprochement with the United States.