Edexcel IGCSE History: A World Divided, Superpower Relations, 1943–72 (4HI1)

“A world divided: superpower relations, 1943–72” is Depth Study 6 on Paper 1 of Pearson Edexcel International GCSE History (4HI1). It explains how the wartime alliance of the USA, Britain and the USSR broke down into the Cold War, how tension peaked in crises over Berlin, Hungary, Cuba and Czechoslovakia, and why the superpowers moved towards détente by 1972. You answer one three-part question: extract impression, two effects and a 16-mark essay.

Related: Revision notes | Practice questions | Paper 1 Depth Studies overview

Syllabus coverage

The 4HI1 specification (Issue 5, February 2026) sets five key topics:

1. Reasons for the Cold War — long-term rivalry and the ideological gap between communism and capitalism, wartime tensions, the Tehran, Yalta and Potsdam conferences, the USSR and Eastern Europe, and the attitudes of Truman and Stalin.
2. Early developments, 1945–49 — Soviet expansion, the “iron curtain”, the Truman Doctrine and Marshall Plan, Cominform and Comecon, Bizonia, the Berlin Crisis (1948–49), NATO and the creation of the FRG and GDR.
3. The Cold War in the 1950s — the Korean War and the Warsaw Pact, Khrushchev and peaceful co-existence, Hungary (Rákosi, de-Stalinisation, Nagy, the Soviet invasion and its effects), and the nuclear arms race.
4. Three crises: Berlin, Cuba and Czechoslovakia — the U2 incident and the Paris Summit, the Berlin Wall (1961), the Bay of Pigs and the Cuban Missile Crisis, and the invasion of Czechoslovakia and the Brezhnev Doctrine.
5. The Thaw and moves towards détente, 1963–72 — the Hotline, the Test Ban, Outer Space and Non-proliferation Treaties, reasons for détente, the SALT talks and treaty, and the extent of détente in 1972.

Why did the Cold War begin?

The USA and USSR had opposed ideologies: capitalism and liberal democracy against communism and one-party rule. Distrust went back to 1917 and Western intervention in the Russian Civil War, and Stalin resented the delay in opening a second front in Europe during the war.

At Tehran (November–December 1943), Churchill, Roosevelt and Stalin agreed on a second front in France and that Poland’s borders would move westward. At Yalta (February 1945) they agreed to divide Germany and Berlin into zones, to hold free elections in liberated Europe (the Declaration on Liberated Europe), to set up the United Nations, and that the USSR would join the war against Japan. At Potsdam (July–August 1945) relations were worse: Roosevelt had died and Truman, more suspicious of Stalin, had replaced him; Attlee replaced Churchill during the conference. The leaders argued over reparations and Poland, and Truman told Stalin about a powerful new weapon — the atomic bomb dropped on Hiroshima days later. Stalin wanted a buffer zone of friendly states to protect the USSR from future invasion; Truman saw this as communist expansion.

How did the division of Europe develop, 1945–49?

Communist-dominated governments took power across Eastern Europe, ending with the coup in Czechoslovakia (February 1948). In March 1946 Churchill warned at Fulton, Missouri, that an “iron curtain” had descended across Europe. In March 1947 the Truman Doctrine promised support for free peoples resisting subjugation, beginning with aid to Greece and Turkey: the policy of containment. The Marshall Plan (announced June 1947) offered economic aid to rebuild Europe; Stalin refused it for the Eastern bloc, calling it “dollar imperialism”, and set up Cominform (1947) and Comecon (1949) in response.

Britain and the USA merged their German zones into Bizonia (1947), and a new currency was introduced in the western zones in June 1948. Stalin responded with the Berlin Blockade (June 1948–May 1949), cutting land routes to West Berlin; the Western allies supplied the city by the Berlin Airlift until Stalin lifted the blockade. Results: the creation of NATO (April 1949), and the division of Germany into the Federal Republic (FRG) and the German Democratic Republic (GDR) in 1949.

How did the Cold War change in the 1950s?

The Korean War (1950–53) spread the Cold War to Asia and boosted military spending. West Germany joined NATO in 1955 and the Soviet bloc formed the Warsaw Pact the same year. After Stalin’s death Khrushchev spoke of peaceful co-existence and in his Secret Speech of February 1956 attacked Stalin, encouraging hopes of change in Eastern Europe.

In Hungary, the Stalinist leader Rákosi had ruled through the secret police. In October 1956 protests brought Imre Nagy to power; he promised free elections and announced Hungary would leave the Warsaw Pact. Soviet tanks crushed the rising in November 1956; thousands were killed, around 200,000 fled, and Nagy was later executed. The West condemned the invasion through the UN but did not intervene — showing that the USA would not challenge the Soviet sphere.

The nuclear arms race intensified: the USSR tested an atomic bomb in 1949, both sides developed hydrogen bombs, and the Soviet launch of Sputnik (1957) suggested a lead in missiles. Fear of nuclear war made both sides cautious but also raised the stakes of every crisis.

What were the three crises of the 1960s?

Berlin. The U2 incident (May 1960), when an American spy plane was shot down over the USSR, wrecked the Paris Summit. Around three million people had left the GDR by 1961, many through Berlin, so in August 1961 the GDR built the Berlin Wall. It stopped the refugee flow and became a symbol of division; Kennedy’s visit in 1963 (“Ich bin ein Berliner”) showed US commitment.

Cuba. After Castro’s revolution, the CIA-backed Bay of Pigs invasion (April 1961) failed. In October 1962 US spy planes found Soviet missile sites in Cuba. Kennedy announced a naval “quarantine”; after thirteen days Khrushchev agreed to remove the missiles in return for a US pledge not to invade Cuba and a secret promise to remove US missiles from Turkey. The crisis showed how close nuclear war could come.

Czechoslovakia. In the Prague Spring (1968) Dubček introduced “socialism with a human face”. Warsaw Pact forces invaded in August 1968. The Brezhnev Doctrine declared that the bloc would intervene wherever socialism was threatened.

Why did relations thaw, and how far did détente go by 1972?

After Cuba a Hotline (1963) linked Washington and Moscow, and the Partial Test Ban Treaty (1963) ended nuclear tests in the atmosphere. The Outer Space Treaty (1967) banned nuclear weapons in space, and the Nuclear Non-proliferation Treaty (1968) aimed to stop their spread. Reasons for détente included the cost of the arms race, the US war in Vietnam, the Sino-Soviet split and the fear created by Cuba. The SALT talks from 1969 produced the SALT I agreements (May 1972), limiting anti-ballistic missiles and freezing numbers of strategic missiles. Détente was real but limited: rivalry continued in Vietnam and elsewhere, and SALT I did not reduce existing arsenals.

Frequently asked questions

Who was to blame for the Cold War? A classic essay. Weigh Soviet expansion in Eastern Europe against US containment, the atomic bomb and the Marshall Plan.

Why was the Berlin Wall built? Mainly to stop the loss of skilled workers from the GDR through West Berlin.

Did the Cuban Missile Crisis cause détente? It was a major reason, but cost, Vietnam and the Sino-Soviet split also mattered.

Official syllabus

Pearson Edexcel International GCSE History (4HI1) specification, Issue 5, February 2026, Paper 1, Depth Study 6 — qualifications.pearson.com.