pressure on the government to exercise more foreign policy initiatives independent of the United States, without, however, compromising vital security and economic ties. The so-called Nixon "shock," involving the surprise visit to China by Richard Nixon and the sudden reconciliation in Sino-American relations, also argued for a more independent Japanese foreign policy. A similar move in Sino-Japanese relations followed. The nation's phenomenal economic growth had made it a ranking world economic power by the early 1970s and had generated a sense of pride and self-esteem, especially among the younger generation. The demand for a more independent foreign policy reflected this enhanced self-image. On the other hand, Japan's burgeoning economic growth and expansion into overseas markets had given rise to foreign charges of "economic aggression" and demands that it adopt more balanced trade policies. Changes in the power relationships in the Asia-Pacific quadrilateral—made up of Japan, the People's Republic of China, the United States, and the Soviet Union—also called for reexamination of policies. The deepening Sino-Soviet split and confrontation, the dramatic rapprochement between the United States and China, the rapid reduction of the United States military presence in Asia following the Vietnam War (Second Indochina War, 1954–75), and the 1970s expansion of Soviet military power in the western Pacific all required a reevaluation of Japan's security position and overall role in Asia. The move toward a more autonomous foreign policy was accelerated in the 1970s by the United States decision to withdraw troops from Indochina. Japanese public opinion had earlier favored some distance between Japan and the United States involvement in war in Vietnam. The collapse of the war effort in Vietnam was seen as the end of United States military and economic dominance in Asia and brought to the fore a marked shift in Japan's attitudes about the United States. This shift, which had been developing since the early 1970s, took the form of questioning the credibility of the United States nuclear umbrella, as well as its ability to underwrite a stable international currency system, guarantee Japan's access to energy and raw materials, and secure Japan's interests in a stable political order. The shift therefore required a reassessment of omnidirectional diplomacy. Changes in world economic relations during the 1970s also encouraged a more independent stance. Japan had become less dependent on the Western powers for resources. Oil, for example, was obtained directly from the producing countries in the Middle East