With the end of the Korean War in 1953, the United States and the Soviet Union each spent huge sums of money and manpower building up their arsenal of nuclear weapons and military forces. They did not engage directly on the battlefield, but they attempted to spread their influence around the world while protecting their spheres of influence closer to their borders. The growing presence of nuclear weapons hung over diplomatic crises wherever they emerged, occasionally prompting the leaders of the two most powerful nations to seek an accommodation.