China

In January 1979, the United States and Communist China established formal diplomatic relations. The U.S. broke diplomatic relations with Taiwan thereby meeting the Communist Chinese precondition for the reestablishment of diplomatic relations..

January 1, 1979, marked a historic pivot in the geopolitics of the late 20th century as the United States of America and the People's Republic of China (PRC), ruled by the Communist Party, established formal diplomatic relations. This move concluded nearly three decades of non-recognition and hostilities following the Chinese Communist Revolution in 1949.

During the period of non-recognition, the United States maintained diplomatic relations with the Republic of China (ROC), situated in Taiwan. Following the civil war in China, the ROC had lost the mainland to the communist forces led by Mao Zedong, but continued to claim sovereignty over all of China, including the mainland. The US, along with many other Western countries, supported this claim.

However, the geopolitical landscape began to change in the late 1960s and early 1970s. The Cold War context saw the U.S. strategically interested in creating a triangular balance of power among the US, the Soviet Union, and China. This was to deter a possible Soviet-Chinese alliance, which could have posed a significant threat to the United States. Thus, began President Richard Nixon's efforts towards rapprochement with the PRC.

The process reached a milestone in February 1972 when President Nixon visited China, signaling a thaw in relations. The groundwork for establishing diplomatic relations was laid during this visit, which was followed by several years of negotiations.

The U.S.-China Joint Communiqué on the Establishment of Diplomatic Relations, signed on December 15, 1978, and effective from January 1, 1979, marked the culmination of these efforts. However, the precondition set by the PRC for formalizing these relations was the severance of all diplomatic relations with Taiwan by the United States. This precondition was based on the PRC's One-China policy, which asserts that there is only one China, including Taiwan, and that the PRC is the only legitimate representative of China.

Complying with this precondition, the U.S. discontinued diplomatic relations with Taiwan. This was a significant departure from the U.S.' long-standing policy, triggering considerable controversy. However, the U.S. assured it would continue its economic and cultural relations with Taiwan, leading to the enactment of the Taiwan Relations Act in April 1979. This act maintains de facto relations with Taiwan, allowing the U.S. to provide the island with defensive arms and stating that any threats to Taiwan would be considered of grave concern to the U.S.

The formal establishment of U.S.-China diplomatic relations in 1979 marked a watershed in international relations. It not only realigned global alliances but also contributed to China's integration into the global economy. Nevertheless, the move has also led to ongoing complexities concerning the U.S.' relationship with Taiwan, a matter which continues to be a sensitive issue in U.S.-China relations.