Explain why the wartime alliance between the USA and the USSR broke down into a Cold War after 1945

What this dot point is asking

SEAB wants you to explain why the wartime alliance between the United States and the Soviet Union, which had together defeated Nazi Germany, broke down into hostility after 1945, beginning the Cold War. You should be able to explain the deep ideological differences between the two superpowers, why their alliance was only ever temporary, and the specific disputes (especially over Eastern Europe and Germany) that turned suspicion into open rivalry. The task is explanation: link the underlying differences and the events of 1945 onward to the breakdown of cooperation.

The answer

Allies only against a common enemy

During the Second World War, the United States and the Soviet Union were allies, part of the "Grand Alliance" with Britain that defeated Nazi Germany. But this alliance was always a marriage of convenience. The two countries had completely opposite political and economic systems and had distrusted each other for years before the war. They cooperated only because they faced a common enemy in Hitler. Once Germany was defeated in 1945, that shared purpose disappeared, and the underlying differences quickly came to the surface.

The clash of ideologies

The deepest cause of the breakdown was a clash of ideologies, meaning opposite beliefs about how society should be run. The United States was a capitalist democracy: it believed in free elections, individual freedom, private business and free trade between nations. The Soviet Union, under Stalin, was a communist one-party state: it believed in state control of the economy, rule by the Communist Party, and the eventual spread of communism around the world. Each side saw the other's system as a threat. Americans feared communism would spread and destroy freedom and free enterprise; the Soviets feared capitalism wanted to surround and destroy communism. This mutual fear made deep distrust almost inevitable.

Suspicion built up during the war

Suspicion had roots even during the war. The Western powers and the Soviet Union did not fully trust one another. Stalin resented that the Western Allies delayed opening a major second front in western Europe until 1944, leaving the Soviet Union to bear the brunt of the fighting against Germany for years. The Soviets were also suspicious that the Americans had developed the atomic bomb in secret. For their part, the Western powers were wary of Stalin's intentions and his record of brutality. So even before the war ended, the partners eyed each other with caution.

Disagreement over Eastern Europe

The sharpest dispute after the war was over the future of Eastern Europe. As the Soviet army drove the Germans back, it occupied much of Eastern Europe, including Poland. At the wartime conferences (Yalta and Potsdam in 1945) the Allies had discussed the future of these countries, and there was talk of free elections. But Stalin was determined to control Eastern Europe as a protective buffer zone, because Germany had invaded the Soviet Union through this region. Soviet-backed communist governments were installed across Eastern Europe. To the West, this looked like a broken promise and aggressive expansion; to Stalin, it was essential security. This clash over Eastern Europe, more than anything, turned suspicion into open hostility.

The wartime conferences and growing tension

The strains were visible at the wartime conferences. At Yalta in early 1945 the Big Three (Roosevelt, Churchill and Stalin) still cooperated and agreed broad plans, but disagreements over Poland were already showing. By the Potsdam Conference in mid-1945, the mood had hardened: Roosevelt had died and been replaced by the more suspicious Truman, Germany was defeated, and the powers clashed over Germany and Eastern Europe. Soon after, in 1946, Churchill warned that an "iron curtain" had descended across Europe, dividing the communist east from the free west. Within a year or two of victory, the wartime allies had become Cold War rivals.

Examples in context

Example 1. The "iron curtain" speech. In 1946 Winston Churchill declared that an "iron curtain" had descended across Europe, dividing the Soviet-controlled communist east from the free west. The phrase captured how quickly the wartime alliance had collapsed into division. It became a powerful image of the new Cold War split of Europe and showed how Western leaders now saw the Soviet Union as a threat rather than a partner.

Example 2. Stalin's buffer zone. The Soviet Union had been invaded through Eastern Europe with devastating losses, so Stalin was determined to control the region as a protective barrier against any future attack. By installing friendly communist governments in Poland and other states, he created this buffer. Understanding this motive helps explain why Stalin acted as he did, and why the question of who was to blame for the Cold War is debated.

Try this

Q1. What is meant by the "iron curtain"? [3 marks]

• Cue. Churchill's phrase (1946) for the divide between the Soviet-controlled communist countries of Eastern Europe and the free west.

Q2. Explain why the United States and the Soviet Union distrusted each other after 1945. [5 marks]

• Cue. They held opposite ideologies (capitalism and democracy versus communism), each fearing the other's system; wartime suspicions and the quarrel over Soviet control of Eastern Europe deepened the distrust.

Q3. "The Cold War began mainly because of the clash of ideologies." How far do you agree? [8 marks]

• Cue. Argue ideology was the deepest cause, but weigh it against the loss of the common enemy and the specific disputes over Eastern Europe and Germany before judging.