Why did the Cold War start? A: At the end of World War II, the Soviet Union and the United States competed for global influence and power. B: At the start of World War II, Hitler's pact with Stalin forced the United States to attack the Soviets before they joined the Allies. C: At the end of World War II, Stalin believed that the United States and other western democracies were preparing to attack. D: At the end of the Korean War, the Soviet Union believed the United States had successfully stopped the spread of communism in Asia.