and not from the Western-controlled multinational companies. Other important materials also came increasingly from sources other than the United States and its allies, while trade with the United States as a share of total trade dropped significantly during the decade of the 1970s. But the oil crises of the 1970s sharpened Japanese awareness of the country's vulnerability to cutoffs of raw material and energy supplies, underscoring the need for a less passive, more independent foreign policy. Thus, political leaders began to argue that in the interests of economic self-preservation, more attention should be paid to the financial and development needs of other countries, especially those that provided Japan with vital energy and raw material supplies. Soon after, in the troublesome year of 1979, Japan's leaders welcomed the reassertion of United States military power in Asian and world affairs following the Islamic revolution in Iran, the Teheran hostage crisis, and the Soviet military invasion of Afghanistan. Japanese leaders played a strong supporting role in curbing economic and other interaction with the Soviet Union and its allies in order to help check the expansion of Soviet power in sensitive areas among the developing world countries. 1980s Japanese thinking on foreign policy was also influenced by the rise of a new postwar generation to leadership and policy-making positions. The differences in outlook between the older leaders still in positions of power and influence and the younger generation that was replacing them complicated formulation of foreign policy. Under Prime Minister Yasuhiro Nakasone, a more hawkish stance on foreign policy was introduced. Japan built up a close political-military relationship with the United States as part of a de facto international front of a number of developed and developing countries intent on checking Soviet expansion. Japan's defense spending continued to grow steadily despite overall budgetary restraint. Japan became increasingly active in granting foreign assistance to countries of strategic importance in east–west competition. The realignment of United States and Japanese currencies in the mid-1980s increased the growth of Japanese trade, aid, and investment, especially in Asia. It also accelerated the reversal of the United States fiscal position, from one of the world's largest creditors in the early 1980s to the world's largest debtor at the end of the decade. Japan became the world's largest creditor, an increasingly active investor in the United States, and a major contributor to international debt relief, financial institutions, and other assistance efforts.