President Richard Nixon visited China in 1972 in order to gain an advantage in the Cold War with the Soviet Union. China was also a communist nation, but in the 1950s and 1960s some distance had developed between the USSR and China in their relationship.
Nixon's administration was also in the process of withdrawing US troops from the war in Vietnam, and establishing a relationship with China would give the US a different opportunity for influence in Asia.
Nixon also was in the midst of domestic difficulties with the Watergate scandal, so making a significant move in foreign policy, such as opening relations with communist China, was a way to enhance his presidency at that time.
Nixon's visit to China was a significant event in changing the dynamics of the Cold War and the United States' posture toward communist countries in general.
