The Grand Alliance and early tension

The USA and the Soviet Union (USSR) believed in opposite ideologies:

Significance: each side believed its system was right, and saw the other as a threat to its way of life.

In the Second World War, Britain, the USA and the USSR fought together against Nazi Germany. This was the Grand Alliance. Its leaders, the 'Big Three', were Churchill (Britain), Roosevelt (USA) and Stalin (USSR).

The USSR joined after Germany invaded it in June 1941, and the USA after Japan attacked Pearl Harbor in December 1941.

Cause of later tension: the alliance was held together only by a common enemy. Stalin distrusted the West, and resented that Britain and the USA took until 1944 to invade France, while the Soviet Union did most of the fighting against Germany.

The Big Three met to plan the war and the peace.

Tehran, November–December 1943

• Agreed: Britain and the USA would open a second front by invading France; the USSR would fight Japan once Germany was beaten; Poland's borders would move west.
• Tension: little in public, but Roosevelt and Churchill disagreed about where to attack, and Stalin was left to shape Eastern Europe.

Yalta, February 1945

• Agreed: Germany and Berlin would each be divided into four zones; there would be free elections in liberated Eastern Europe; the USSR would join the new United Nations and fight Japan.
• Tension: who would govern Poland. Stalin wanted a communist government friendly to the USSR.

By Potsdam, the leaders had changed. Roosevelt had died in April 1945, and Truman, who was much more suspicious of Stalin, replaced him. During the conference, Churchill lost the British election and was replaced by Attlee.

• Agreed: the four zones of Germany and Berlin; the Nazi Party banned and war criminals put on trial; Germany to pay reparations, mostly from each power's own zone; Poland's new western border.
• Tension: how much Germany should pay; Soviet troops still controlling Eastern Europe; and Truman told Stalin about a powerful new weapon without saying what it was.

Change: the friendship of the war had become suspicion.

• Stalin wanted security. Russia had been invaded from the west twice in 30 years, and many millions of Soviet people died in the Second World War. He wanted friendly, communist governments in Eastern Europe as a buffer zone.
• Truman was strongly anti-communist. He believed Stalin was trying to spread communism, and that the USA should stand up to him.
• Churchill distrusted Stalin. In March 1946, in a speech in the USA, he warned that an 'iron curtain' had come down across Europe, dividing the free West from the Soviet-controlled East.

Cause: what Stalin saw as defence, the West saw as expansion.

In August 1945 the USA dropped atomic bombs on Hiroshima and Nagasaki, and Japan surrendered. The USA was now the only country with nuclear weapons. Stalin saw it as a threat, and sped up the Soviet bomb project.

In 1946, each side's diplomats sent home reports about the other:

• The Long Telegram (February 1946), from George Kennan in Moscow, said the USSR was determined to spread communism and would only back down when faced with strength.
• The Novikov Telegram (September 1946), from Soviet ambassador Nikolai Novikov in Washington, said the USA wanted to dominate the world and was preparing for war.

Significance: each side's leaders now saw the other as aggressive, so they prepared to resist it.