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The big idea: The USA and USSR fought Hitler together, then fell out fast. Deep differences in belief, and the collapse of a fragile wartime friendship, turned allies into rivals.
During the Second World War, the USA, the USSR and Britain joined forces to beat Nazi Germany. Historians call this the Grand Alliance.
But it was never a true friendship. It was a marriage of convenience — three very different countries teaming up against one shared enemy.
Once that enemy was defeated in 1945, the glue holding them together was gone. The old suspicions came flooding back.
To understand why, you first have to see how differently the USA and USSR saw the world.
The USA — capitalism and democracy
- Liberal democracy — people vote in free elections and choose between rival parties
- Capitalism — private businesses and individuals own factories, farms and shops
- A market economy — prices and production are set by supply and demand, not the state
- Believed its way of life should spread and trade should be free
The USSR — communism and one-party rule
- A one-party state — only the Communist Party was allowed; no free elections
- Communism — the state owns the factories, land and businesses on behalf of the people
- A command economy — the government plans and controls what gets made and at what price
- Believed capitalism was doomed and communism would one day spread worldwide
Why this mattered so much: These were not small disagreements. Each side thought the other's system was a threat to its own survival.
The Americans feared communism would spread across the globe. The Soviets feared the capitalist West wanted to destroy them, as the West had tried to do after the 1917 Russian Revolution.
Spot it fast: two opposite worlds: USA = free elections + private business + market prices.
USSR = one party + state ownership + planned economy. Opposite in almost every way.
Ideology set the stage, but real events during the war planted the seeds of mistrust. Each side did things the other saw as a betrayal.
Here are the big ones.
1 · The delayed Second Front
Stalin begged Britain and the USA to invade Western Europe early, to draw German troops away from Russia. The Soviets were doing most of the dying, losing millions. But the Western invasion (D-Day) did not come until June 1944. Stalin suspected his allies were happy to let the USSR bleed while they waited.
2 · The US atomic monopoly (1945)
In 1945 the USA became the only country with the atomic bomb — and used it on Japan. The Soviets had not even been told about it in advance. To Stalin, this was a threat pointed at the USSR as much as at Japan.
3 · Soviet security fears
Russia had been invaded from the West twice in 30 years, and lost around 27 million people in WWII. Stalin was determined it must never happen again. He wanted friendly, controlled countries around the USSR as a shield.
4 · The Eastern European 'buffer zone'
As the Red Army pushed Germany back, it occupied Poland, Hungary, Romania and more. Stalin wanted these lands as a buffer zone. To the West, this looked like the USSR simply swallowing free nations.
Second Front late · Bomb secret · Fear of invasion · Buffer zone grabbed.
The heart of the clash: Notice how the same fact looked totally different to each side.
To Stalin, the buffer zone was defence — protecting the USSR from future attack. To the USA, it was aggression — the Soviets breaking their promise of free elections and imposing communism by force.
Two ways to read the same map: Imagine you are Stalin in 1945. Your country has just lost 27 million people. You look at Poland — the road every invader has used to attack Russia — and you decide no unfriendly government will ever sit there again.
Now imagine you are in Washington. You see a huge army forcing communist rule on free countries, one after another. Same events, opposite meaning.
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As the war ended, the Big Three leaders met twice to plan the peace. These two meetings show the friendship cooling into rivalry.
The first, at Yalta, was still fairly warm. The second, at Potsdam, was tense and suspicious.
Yalta Conference — February 1945: The war was nearly won, so the mood was cooperative. Present were Roosevelt (USA), Stalin (USSR) and Churchill (Britain).
They agreed on real things: a new United Nations to keep peace; Germany split into four zones; free elections in the countries freed from Nazi rule; and Stalin's promise to join the war against Japan once Germany fell.
The catch at Yalta: The promise of 'free elections' was left vague. Stalin and the West meant very different things by 'free'.
To the West it meant real, competitive votes. To Stalin it meant governments friendly to Moscow. This gap would soon cause bitter arguments.
Potsdam Conference — July to August 1945: By now the mood had changed sharply. The cast was different too: Truman had replaced the late Roosevelt, and Attlee replaced Churchill mid-conference after a UK election. Only Stalin remained.
They clashed over reparations (how much Germany should pay), over Poland's new communist government and borders, and Truman was far tougher — because the USA had just tested the atomic bomb.
| Yalta (Feb 1945) | Potsdam (Jul–Aug 1945) | |
|---|---|---|
| Leaders | Roosevelt, Stalin, Churchill | Truman, Stalin, Attlee |
| Mood | Cooperative — war nearly won | Tense — deep distrust |
| Big issue | UN, German zones, free elections | Reparations, Poland, the bomb |
| Atomic bomb | Not yet tested | Just tested — Truman more confident |
By 1946 the split was open. Two famous moments captured it in words.
Both men warned that Europe was being cut in two, with a hostile communist bloc on one side.
Churchill's 'Iron Curtain' speech — Fulton, USA, 1946
Speaking in Fulton, Missouri, Churchill said an 'iron curtain' had come down across Europe, from the Baltic to the Adriatic. Behind it, the countries of Eastern Europe were falling under Soviet control. The phrase stuck and became the image of a divided Europe.
Kennan's 'Long Telegram' — 1946
George Kennan, a US diplomat in Moscow, sent a long message home. He argued the USSR was deeply hostile, saw the world as us-versus-them, and could not be trusted — so the USA had to firmly resist Soviet expansion. It shaped later US policy.
How this is tested (Paper 2): Paper 2 is essay-based, not source-based. The classic question asks you to weigh the causes of the Cold War — usually ideology against events and personalities.
Don't just narrate Yalta and Potsdam. Argue which factor mattered most and reach a judgement.
Examine the reasons why the wartime Grand Alliance had broken down by 1946.
Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.