From Wikipedia:

The 1972 visit by United States presidentRichard Nixon to the People's Republic of China was an important strategic and diplomatic overture that marked the culmination of the Nixon administration's establishment of relations between the United States of America and the People's Republic of China after years of American diplomatic policy that favored the Republic of China in Taiwan. The seven-day official visit to three Chinese cities was the first time a U.S. president had visited the PRC; Nixon's arrival in Beijing ended 25 years of no communication or diplomatic ties between the two countries and was the key step in normalizing relations between the U.S. and the PRC. Nixon visited the PRC to gain more leverage over relations with the Soviet Union, following the Sino-Soviet split. The normalization of ties culminated in 1979, when the U.S. established full diplomatic relations with the PRC.