Current U.S. strategic planning rests on an assumption that the most likely cause of a major war with the Soviet Union would be a Soviet military attack on the United States or its European allies. This Project AIR FORCE report questions the validity of that assumption. The author examines the Soviet policy of "peaceful coexistence" against the backdrop of the Soviet military buildup over the past 15 years, and offers an alternative hypothesis for the source of war. He argues that the changing military balance has allowed the Soviet Union to adopt a policy designed to undermine the strategic position of the United States by means short of a direct attack. Effects of this policy are to disrupt global stability and encourage situations in critical areas that might bring about American intervention. This could precipitate a military confrontation with the Soviet or Soviet-supported forces, and become a more likely source of war between the two superpowers than a direct Soviet attack on the United States or its allies. U.S. defense policy has not made adequate allowance for this contingency.