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NotesHistoryTopic 16.3Effects of the Second World War (1939–45)
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16.3.33 min read

Effects of the Second World War (1939–45)

IB History • Unit 16

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Contents

  • Peacemaking and a new world order
  • Territorial and political effects
  • Human, economic and social effects

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The big idea: The Second World War did not end with a single peace treaty like WWI did. Instead, the winners met during the war to plan the peace.

At Yalta and Potsdam the Allies redrew the map of Europe and set up a brand-new peacekeeping body, the United Nations.

The "Big Three" who shaped the postwar world were the leaders of the USA, the USSR and Britain. At Yalta in February 1945 this meant Roosevelt, Stalin and Churchill.

By Potsdam in July 1945 the faces had changed: Roosevelt had died and Truman was now US president, and halfway through the meeting Churchill was voted out and replaced by Attlee.

1

Yalta (Feb 1945)

With victory in sight, the Big Three agreed Germany would be split into occupation zones, Nazis punished, and free elections held in liberated Europe. Stalin promised to join the war on Japan.

2

Potsdam (Jul–Aug 1945)

Germany was now defeated and trust had cooled. They confirmed the zones and Poland's new borders, but argued over reparations and elections — the first cracks of the Cold War.

3

The United Nations (1945)

Founded in October 1945 to replace the failed League of Nations. Its Security Council gave the great powers a veto, so it had real muscle the League never had.

Yalta = planning while winning; Potsdam = arguing after winning.

Why the UN succeeded where the League failed: The League of Nations had no army, worked by unanimous votes, and the USA never joined.

The United Nations fixed all three problems: the USA was a founding member, decisions passed without needing everyone to agree, and members could contribute troops for peacekeeping.

League of Nations (after WWI)

  • USA refused to join
  • Needed unanimous agreement to act
  • No armed force of its own
  • Collapsed in the 1930s

United Nations (after WWII)

  • USA a founding member and host
  • Security Council with five permanent powers
  • Could call on member states' troops
  • Still functioning today

The war completely rearranged the map and the balance of power. Two changes mattered most: Germany was divided, and the Soviet Union took control of Eastern Europe.

Out of this grew a new, tense rivalry that would dominate the next 45 years — the Cold War.

  • Division of Germany — split into four occupation zones (US, British, French, Soviet); Berlin, deep inside the Soviet zone, was also divided four ways.
  • Poland moved west — its eastern land went to the USSR, and it was compensated with German land in the west, shifting the whole country hundreds of kilometres.
  • Soviet control of Eastern Europe — the Red Army had liberated countries like Poland, Hungary and Czechoslovakia, and Stalin installed friendly communist governments there.
  • The Iron Curtain — Churchill's 1946 phrase for the line splitting a free West from a Soviet-controlled East.
The onset of the Cold War: The wartime alliance had only held together because both sides hated Hitler more than each other.

Once Germany fell, the USA and USSR — superpowers with opposite systems, capitalism versus communism — became rivals. This standoff, fought through threats, spying and proxy wars rather than direct battle, is the Cold War.

Two superpowers replace the old great powers

Britain, France and Germany were exhausted and broke. The USA (with the atomic bomb and half the world's wealth) and the USSR (with the largest army in Europe) now towered over everyone else.

Decolonisation accelerates

The war shattered the myth that European empires were unbeatable, drained their treasuries, and inspired independence movements. India became independent in 1947, and much of Asia and Africa followed over the next two decades.

Communist expansion

Communism spread across Eastern Europe under Soviet control, and in 1949 the world's most populous nation, China, turned communist under Mao — alarming the West.

Link the effects together: Strong Paper 2 answers connect these changes: the rise of the superpowers, the division of Germany and the spread of communism are not separate facts — together they are the beginning of the Cold War. Show the chain, don't just list.

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The human cost: The Second World War was the deadliest conflict in history: an estimated 50–70 million or more people died.

Unlike WWI, the majority were civilians — killed by bombing, starvation, disease and deliberate mass murder, including the Holocaust.
CountryApprox. deathsNote
USSR~27 millionBy far the heaviest losses of any nation
China~15–20 millionMostly from the long war with Japan
Germany~7 millionMilitary and civilian
Jewish victims~6 millionThe Holocaust, across all countries

The war left Europe and Asia in ruins. Cities like Warsaw, Dresden and Hiroshima were flattened, and factories, railways and farms lay wrecked.

Into this devastation the USA poured money through the Marshall Plan of 1948 — around 13 billion dollars to rebuild Western Europe, revive trade, and (not by accident) keep those countries out of communist hands.

  • Devastation — whole cities destroyed, economies collapsed, millions homeless and hungry.
  • Marshall Plan (1948) — massive US aid rebuilt Western Europe and tied it to the American, capitalist bloc.
  • Displacement — tens of millions became refugees, pushed across new borders as populations were expelled and resettled.
  • Women's changing role — with men at the front, women had run factories, farms and services; this pushed forward, though unevenly, their place in work and society.
The further transformation of women's role: During the war women filled jobs once reserved for men — building tanks and aircraft, driving buses, working the land.

Many were pushed back home when the men returned, but the war had proved women could do this work. It strengthened arguments for equality and helped lay the ground for later feminist movements.
The legacy: justice and a new framework: At the Nuremberg Trials (1945–46) leading Nazis were put on trial for war crimes and crimes against humanity — a landmark that said leaders could be held personally responsible.

Together with the UN, this created a new framework of international relations built on human rights and international law.

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16.1.1Types and causes of war: the framework
16.1.2Causes of the First World War (1914–18)
16.1.3Causes of the Second World War (1939–45)
16.2.1How wars are fought: the framework
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