After reaching extremes of isolation in the wake of the Great Leap Forward and again during the tumultuous Cultural Revolution years of the late 1960s, China's links with the world economic community began to expand in the early 1970s. This can be seen in the expansion of trade beyond the peak levels of the late 1950s, in China's admission to the United Nations in 1970, and in the gradual development of diplomatic ties signaled by the "ping-pong diplomacy" of 1971 and President Richard Nixon's visit to China in 1973.