The wartime alliance breaks down, 1945

The USA and the USSR were allies of necessity, divided by ideology: American capitalism and democracy against Soviet communism and one-party rule.

• Yalta (February 1945): agreement to divide Germany into zones, to establish the United Nations, and to allow free elections in liberated Europe.
• Potsdam (July–August 1945): Roosevelt had died, Churchill was replaced mid-conference, and Truman took a harder line. Disputes over Poland, reparations and Soviet behaviour in Eastern Europe were open.
• Hiroshima and Nagasaki (August 1945): the USA used atomic bombs against Japan. Stalin read the bomb as a threat as well as a weapon, and accelerated the Soviet nuclear programme.

Why did the alliance collapse?

Eastern Europe, containment and Berlin

• Soviet takeover: between 1945 and 1948, communist governments were installed across Eastern Europe, backed by the Red Army. Free elections promised at Yalta did not materialise.
• Iron Curtain: in March 1946 Churchill declared that an iron curtain had descended across the continent.
• The American response (1947): the Truman Doctrine — the USA would support free peoples resisting subjugation (containment) — and the Marshall Plan — massive economic aid to rebuild Western Europe and make communism less attractive. Stalin forbade the satellites to accept it.
• The Berlin Blockade (June 1948 – May 1949): Stalin cut road, rail and canal links to West Berlin after the Western powers introduced a new currency. The West mounted the Berlin Airlift, flying in supplies for eleven months. Stalin backed down.
• Consequences: Germany was formally split into West and East; NATO was founded in 1949; the Warsaw Pact followed in 1955.

The Marshall Plan

Hungary, Berlin and Czechoslovakia

• Hungary, 1956: Imre Nagy promised free elections and announced withdrawal from the Warsaw Pact. Soviet tanks crushed the rising; thousands died and 200,000 fled. The West protested but did not intervene — it was distracted by Suez and unwilling to risk war.
• Berlin, 1959–61: skilled workers were escaping to the West through Berlin in huge numbers, embarrassing and weakening East Germany. In August 1961 the Berlin Wall was built. It stopped the exodus — and became the Cold War's defining symbol.
• Czechoslovakia, 1968: Alexander Dubček's "socialism with a human face" (the Prague Spring) relaxed censorship and promised reform. Warsaw Pact forces invaded in August. The Brezhnev Doctrine declared the USSR's right to intervene wherever socialism was threatened.

The pattern that shaped relations: the USSR would use force inside its bloc; the West would protest but not fight for Eastern Europe. Each crisis deepened distrust without triggering war — the essence of the Cold War.

Sort the Cold War crises

Tap a crisis, then tap where it happened.

Korea, Vietnam, Cuba and Afghanistan

• Korea, 1950–53: North Korea invaded the South. The USA led a UN force (the USSR was boycotting the Security Council and could not veto). China intervened when UN troops neared its border. The 1953 armistice left the country divided close to the 38th parallel.
• Vietnam, 1950–73: the USA backed the South against the communist North. After the Gulf of Tonkin incident (1964), it committed huge forces; the Tet Offensive (1968) shattered US confidence, and television coverage turned opinion at home. The USA withdrew under the Paris Peace Accords (1973); the North won in 1975.
• Cuba, 1959–62: Castro's revolution, the failed Bay of Pigs (1961), and then the Cuban Missile Crisis of October 1962 — the closest the world came to nuclear war. Kennedy blockaded Cuba; Khrushchev withdrew the missiles in return for a pledge not to invade Cuba (and the quiet removal of US missiles from Turkey). A telephone hotline and test-ban talks followed.
• Afghanistan, 1979–89: the USSR invaded to prop up a communist government and became bogged down against the US-backed mujahideen. The war drained Soviet resources and morale — and ended détente.

When was the Cuban Missile Crisis?

Gorbachev, Reagan and 1989–91

Mikhail Gorbachev came to power in 1985 facing a stagnant economy, the cost of the arms race and the drain of Afghanistan.

• Glasnost (openness) allowed criticism and loosened censorship; perestroika (restructuring) tried to reform the economy.
• Gorbachev pursued arms control with President Reagan and made clear the USSR would not use force to keep the satellite regimes in power.
• In 1989 communist governments fell across Eastern Europe; the Berlin Wall opened on 9 November 1989, and Germany was reunified in 1990.
• The Soviet Union itself dissolved in 1991. The Cold War was over.

Match the crisis to its consequence

Tap a crisis on the left, then its main consequence on the right.

9/11, Afghanistan and Iraq

• Consequences of the Soviet war: Afghanistan was left shattered. Out of the chaos came the Taliban, who took power in the 1990s, and a base for al-Qaeda under Osama bin Laden.
• 11 September 2001: al-Qaeda hijackers flew aircraft into the World Trade Center and the Pentagon; a fourth aircraft crashed in Pennsylvania. Nearly 3,000 people were killed.
• Afghanistan, 2001: when the Taliban refused to hand over bin Laden, a US-led coalition invaded, toppling the Taliban government. NATO invoked its collective defence clause for the first time.
• Iraq, 2003: a US-led coalition, including Britain, invaded Iraq, arguing that Saddam Hussein held weapons of mass destruction and supported terrorism. Saddam's regime fell within weeks; no stockpiles of such weapons were found. The invasion had no explicit UN Security Council authorisation and divided world opinion, straining relations even between allies.

Why did the Iraq War divide opinion?

Writing about impact on relations

CCEA Unit 2 keeps asking one thing: what was the impact on international relations? Build every answer the same way:

• Causes — why did the crisis happen?
• Events — the key actions, with dates.
• Consequences — what changed between the powers: alliances formed, trust lost or rebuilt, arms agreements, new hostility.

Example: the Cuban Missile Crisis. Cause — Soviet missiles in Cuba after the Bay of Pigs. Events — blockade, thirteen days, withdrawal. Impact — both sides, shocked by how close they came, set up a hotline and moved towards the 1963 test-ban treaty.

When did the Berlin Wall open?

The Brezhnev Doctrine

The shape of 1945–2003

Three phases to hold in your head:

• 1945–49 — the Cold War begins: ideological split, the Soviet takeover of Eastern Europe, containment, Berlin, NATO.
• 1950–89 — confrontation without direct war: proxy wars (Korea, Vietnam, Afghanistan), crises (Cuba), and repression inside the Soviet bloc (Hungary, Czechoslovakia) — until Gorbachev refused to use force.
• 1991–2003 — a new age of conflict: American dominance, then 9/11, the "war on terror", Afghanistan and the divisive invasion of Iraq.

Why did the Berlin Wall go up?

The big ideas to know

That is CCEA Unit 2: International Relations, 1945–2003. Press Finish to see your score.