1939-1945: The War That Remade the World

The Second World War killed more people than any conflict in history, introduced the atomic bomb, and ended with the world divided between two superpowers. It was not a bolt from the blue: it grew directly out of the unresolved business of 1919, a punishing peace, a collapsed economy, a failed League, and dictators the democracies refused to stop. For UPSC, 1939-45 is the bridge between the world wars and everything after: the United Nations, the Cold War, and decolonisation all begin here.

Why the peace failed: the causes

The war's roots lay in the settlement of 1919. The Treaty of Versailles, war guilt, reparations, territorial losses, disarmament, bred a resentment in Germany that Hitler converted into a political weapon. The problem of national minorities gave him his pretexts: German populations in Poland and Czechoslovakia became the excuse for each successive aggression.

The Great Depression then demolished the fragile recovery of the late 1920s, discrediting democracies and carrying extremists to power in Germany, Italy and Japan. The League of Nations proved unable to stop aggression, Japan in Manchuria (1931), Italy in Abyssinia (1935), because it had no army, no American member, and members unwilling to act. Appeasement completed the disaster: Britain and France tolerated the remilitarisation of the Rhineland (1936), the Anschluss with Austria (1938) and the dismemberment of Czechoslovakia at Munich (1938), teaching Hitler that aggression paid.

The aggressors organised themselves: the Rome-Berlin Axis (1936), the Pact of Steel (1939) with Italy, and the Tripartite Pact (1940) bringing in Japan. Finally, the Nazi-Soviet non-aggression pact of August 1939 neutralised Hitler's fear of a two-front war and cleared the way for the invasion of Poland. When Germany attacked on 1 September 1939, Britain and France declared war two days later, the Second World War had begun.

1939-45: the course of the war

The first phase belonged to the Axis. Using Blitzkrieg, lightning war by tanks and aircraft, Germany crushed Poland, Denmark, Norway, Belgium, the Netherlands and France, which fell in June 1940. But the Battle of Britain (1940) defeated the Luftwaffe, and the planned invasion of England, Operation Sea Lion, was abandoned, Hitler's first great failure.

Between Poland's fall and the 1940 Blitzkrieg lay the Phoney War of 1939-40: eight months in which Britain and France, though formally at war with Germany, launched no major land offensives while Hitler digested Poland. The strange quiet matters because it exposed the Allies' defensive mindset, the same caution that would collapse before the German breakthrough in France.

In 1941 the war became truly global. On 22 June 1941, Germany launched Operation Barbarossa, the invasion of the Soviet Union, the largest military operation in history. Early gains stalled before Moscow amid Soviet resistance and winter. In August 1941, Roosevelt and Churchill issued the Atlantic Charter, sketching post-war principles, and in January 1942 the Declaration of the United Nations formalised the Allied coalition. Then, on 7 December 1941, Japan attacked Pearl Harbor; the United States entered the war, and Germany and Italy declared war on America in return.

1942-43 was the turning point. At Stalingrad, the German Sixth Army was encircled and forced to surrender in early 1943, the beginning of the long Soviet counteroffensive. The Allies cleared North Africa, invaded Sicily, and Italy surrendered in September 1943, though Mussolini lingered on as head of a German-backed rump regime. In June 1944 the western Allies opened the second front with the D-Day landings in Normandy, while Soviet armies liberated Eastern Europe. At Yalta (February 1945), Stalin, Roosevelt and Churchill planned the final assault and the post-war order. Hitler committed suicide on 30 April 1945; Germany surrendered unconditionally on 7 May at Reims, the ceremony repeated in Berlin on 8 May.

The Pacific war ended with terrible finality. After island-hopping campaigns and massive bombing, the United States dropped atomic bombs on Hiroshima (6 August 1945) and Nagasaki (9 August 1945); with the Soviet Union also declaring war on Japan, Tokyo surrendered. The formal Japanese surrender on 2 September 1945 ended the Second World War.

Why did the Axis lose a war it seemed to be winning in 1941? The material balance was decisive once the United States and the Soviet Union were fully engaged: American shipyards and factories outproduced the Axis, Soviet manpower absorbed and then reversed the German invasion, and Britain's empire and sea power kept supply lines open. Strategy compounded the imbalance. Germany fought a two-front war without securing oil or knocking out Britain, Japan struck Pearl Harbor without the industrial depth for a long war, and both regimes treated occupied peoples in ways that turned potential collaborators into resisters. Historians differ on how far ideology made defeat inevitable, but few dispute that after 1942-43 the Axis needed its enemies to make mistakes, and its enemies largely stopped making them.

Home fronts: total war

This was total war, entire societies mobilised. War economies directed industry, rationing governed consumption, and women entered factories and offices in unprecedented numbers, permanently shifting gender roles. Civilians became targets as never before: cities were bombed from London to Dresden to Tokyo, and the Nazi regime murdered six million Jews in the Holocaust alongside millions of others. Science itself was conscripted, most fatefully in the race for the atomic bomb. The suffering was not evenly shared, the Soviet Union bore the heaviest human cost of any nation, but no great power's home front emerged unchanged.

Why the Axis lost

Germany's early brilliance could not overcome arithmetic. The resource imbalance was decisive: America's industrial might, Britain's empire, and a Soviet Union industrialised since 1929 meant that the longer the war lasted, the worse the Axis odds became. Strategic blunders compounded it, above all the two-front war created by invading the USSR while Britain remained undefeated, and Japan's fatal gamble at Pearl Harbor, which brought American power fully into the conflict. Italy proved a weak ally, repeatedly needing German rescue and diverting forces from the Eastern Front. After Stalingrad and Midway, the Axis never regained the initiative.

Battle of Midway (June 1942) was the Pacific war’s decisive turning point: in June 1942 American carriers sank four Japanese aircraft carriers in a single engagement, permanently crippling Japan’s naval air power and shifting the initiative to the United States.

The world remade: consequences

The war's most constructive legacy was the United Nations. Determined not to repeat the League's failure, the Allies built a new organisation with real enforcement teeth: the UN Charter was signed at San Francisco on 26 June 1945 and came into force on 24 October 1945, with a Security Council whose five permanent members wielded the veto.

The global power structure was transformed. Britain and France emerged victorious but exhausted and indebted; the United States and the Soviet Union stood as the two superpowers of a new bipolar order, and their wartime alliance curdled within years into the Cold War. Germany and Austria were divided into four occupation zones; Italy lost its colonies; Japan lost its empire; the USSR absorbed the Baltic states and dominated Eastern Europe. The Marshall Plan (1948) poured American aid into rebuilding Western Europe and anchoring it against communism. The nuclear age had begun, with an arms race already foreseeable. And across Asia and Africa, the war's demonstration that empires could be beaten, plus Europe's visible exhaustion, accelerated decolonisation.

The war also built the economic order. At Bretton Woods in 1944, the Allies designed the post-war financial system: the International Monetary Fund (IMF) to stabilise currencies and the World Bank to fund reconstruction and development, with the US dollar as the anchor currency. It matters because the dollar-based system it created underwrote the West's post-war prosperity and still structures global finance.

Justice followed victory. The Nuremberg Trials (1945-46) put surviving Nazi leaders before an international military tribunal for crimes against humanity, war crimes and waging aggressive war. They matter as the founding precedent of international criminal law: for the first time, state officials were held personally accountable under law, the principle that later produced the International Criminal Court.

Germany's division became permanent. The four occupation zones hardened into two states in 1949: West Germany (the Federal Republic, tied to the Western bloc) and East Germany (the German Democratic Republic, a Soviet satellite), with Berlin itself split and later divided by the Wall. A divided Germany was the Cold War's central geography for forty years, which is why it belongs in any account of the war's consequences.

The question of responsibility remains contested among historians, and UPSC framed it directly in 2015: to what extent can Germany be held responsible for causing the two World Wars? For 1939 the strongest answer separates the trigger, the German invasion of Poland on 1 September 1939, from the deeper causes: Versailles revisionism, Hitler's expansionist programme, the Depression, the failure of the League, and the appeasement that convinced Berlin that Britain and France would not fight.

India and the war

India's contribution was enormous: the British Indian Army grew to 2.5 million volunteers, the largest volunteer force in the world, fighting in Europe, Africa, the Middle East and Southeast Asia, including at Monte Cassino in Italy. India also served as the great supply base for the Allied campaign against Japan. The costs were heavy: some 89,000 Indian soldiers died, wartime inflation and taxation squeezed the economy, and the Bengal famine of 1943 killed millions. Politically, the war radicalised the freedom movement, Subhas Chandra Bose's Indian National Army fought alongside Japan, and the British attempt to try INA men for treason ignited a nationalist upsurge.

The often-quoted figure of 2.5 million refers to the total strength reached by the British Indian Army by August 1945, when it had become the largest volunteer army in history. It is a peak strength figure for the force as a whole, not the number deployed in any single theatre at one time.

Key Terms

• Blitzkrieg: Blitzkrieg is the German method of rapid combined attack by tanks, aircraft and motorised infantry to avoid a long war of attrition.
• Operation Barbarossa: Operation Barbarossa is Germany's invasion of the Soviet Union launched on 22 June 1941.
• Pearl Harbor: Pearl Harbor is the Japanese attack of 7 December 1941 that brought the United States into the Second World War.
• Battle of Stalingrad: Battle of Stalingrad is the 1942-43 battle in which the German Sixth Army was encircled and destroyed, turning the Eastern Front.
• Atlantic Charter: Atlantic Charter is the August 1941 declaration by Roosevelt and Churchill of post-war aims including self-determination.
• United Nations: United Nations is the international organisation founded in 1945 to replace the League and preserve peace through collective security.
• Bretton Woods: Bretton Woods is the 1944 conference that designed the post-war monetary order, creating the IMF and the World Bank.
• Nuremberg Trials: Nuremberg Trials are the 1945-46 trials of major Nazi leaders for war crimes and crimes against humanity.
• Appeasement: Appeasement is the pre-war policy of conceding to Hitler's demands, which failed to prevent war in 1939.
• Tripartite Pact: Tripartite Pact is the 1940 alliance of Germany, Italy and Japan.
• Hiroshima and Nagasaki: Hiroshima and Nagasaki are the Japanese cities destroyed by atomic bombs on 6 and 9 August 1945.
• Quit India Movement: Quit India Movement is the August 1942 movement demanding an immediate end to British rule in India.

For India, the war ended one era and opened another. The Quit India Movement of August 1942 was crushed, but it demonstrated that British authority now rested on force rather than consent. The Indian National Army trials of 1945-46 turned soldiers who had fought Britain into national heroes, the Royal Indian Navy mutiny of February 1946 suggested that the instrument of coercion itself was unreliable, and Britain emerged from the war owing India large sterling balances instead of the other way round. Add the Bengal famine of 1943, in which around three million people are estimated to have died amid wartime inflation, procurement and policy failure, and the political conclusion drawn by Indian leaders was unavoidable: the Raj had neither the capacity nor the legitimacy to rule after 1945. Independence and Partition followed within two years.

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