What was the Cold War? How did the relationship between the United States and the Soviet Union change after World War II?

By the time World War II ended, most American officials agreed that the best defense against the Soviet threat was a strategy called "containment." In his famous "Long Telegram," the diplomat George Kennan (1904-2005) explained the policy: The Soviet Union, he wrote, was "a political force committed fanatically to the belief that with the U. S. there can be no permanent modus vivendi [agreement between parties that disagree]." As a result, America's only choice was the "long-term, patient but firm and vigilant containment of Russian expansive tendencies." "It must be the policy of the United States," he declared before Congress in 1947, "to support free peoples who are resisting attempted subjugation ... by outside pressures." This way of thinking would shape American foreign policy for the next four decades.