Because of the nature of modern weapons, significant innovations in arms technology have the potential to induce dramatic changes in the international distribution of power. Consider, for example, the “strategic defense initiative” (SDI), a program initiated by the United States in the early 1980s. Had the program been successfully completed, it might have led to a substantial devaluation of Soviet nuclear capabilities and put the United States in a very dominant position. It should not then come as a surprise that interstate rivalry, especially among super powers, often takes the form of a race for technological superiority. Mary Acland-Hood claims that although the United States and the Soviet Union together accounted for roughly half of the world's military expenditures in the early 1980s, their share of world military research and development (R&D) expenditures was about 80 percent. As further proof of the perceived importance of R&D, note that whereas the overall U.S. defense budget increased by 38 percent (from $225.1 billion to $311.6 billion in real terms) from 1981 to 1987, military R&D spending increased by 100 percent (from $20.97 billion to $41.96 billion). Moreover, before World War II military R&D absorbed on average less than 1 percent of the military expenditure of major powers, but since then it has grown to 11–13 percent. The emphasis on military technology is bound to become more pronounced in the future as R&D becomes the main arena for interstate competition.