The United States responded by launching a program in 1950 to develop more advanced thermonuclear weapons. On August 29, 1949, the Soviets tested their first nuclear bomb. had obtained-through a network of spies engaging in international espionage-blueprints of a fission-style bomb and discovered regional sources of uranium in Eastern Europe. Within just a few years, however, the U.S.S.R. The Soviets initially lacked the knowledge and raw materials to build nuclear warheads. The United States was the only country with nuclear weaponry in the years immediately following World War II.
