In simple terms, the Cold War could be viewed as an expression of the ideological struggle between communism and capitalism. The United States faced a new uncertainty beginning in September 1949, when it lost its monopoly on the atomic bomb. American intelligence agencies discovered that the Soviet Union had exploded its first atomic bomb, with the consequence that the United States potentially could face a future nuclear war that, for the first time, might devastate its cities. Given this new danger, the United States participated in an arms race with the Soviet Union that included development of the hydrogen bomb, as well as intercontinental strategic bombers and intercontinental ballistic missiles (ICBMs) capable of delivering nuclear weapons. A new fear of communism and its sympathizers swept the United States during the 1950s, which devolved into paranoid McCarthyism. With communism spreading in China, Korea, and Eastern Europe, Americans came to feel so threatened that popular and political culture condoned extensive "witch-hunts" to expose communist spies. Part of the American reaction to the Soviet atomic and hydrogen bomb tests included maintaining a large Air Force, under the control of the Strategic Air Command (SAC). SAC employed intercontinental strategic bombers, as well as medium-bombers based close to Soviet airspace (in western Europe and in Turkey) that were capable of delivering nuclear payloads.