The Second World War joined conflicts across several continents into the most destructive war in modern history. Germany, Italy and Japan pursued expansion for different reasons, while the Allied coalition eventually united Britain and its empire, the Soviet Union, China, the United States and many other states. The alliances changed over time, and the war looked very different in Warsaw, Stalingrad, Burma, London or Manila.
Poland, Scandinavia and the fall of France
Germany invaded Poland on 1 September 1939, using concentrated armour, aircraft and mobile forces to break through defensive positions. The Soviet Union invaded from the east on 17 September under the terms of its pact with Germany. Poland was divided, occupied and subjected to mass violence by both regimes.
After months of limited fighting in the west, Germany invaded Denmark and Norway in April 1940 and attacked the Netherlands, Belgium, Luxembourg and France in May. German forces advanced through the Ardennes, cutting off Allied armies that had moved into Belgium. France signed an armistice in June; Britain evacuated many troops from Dunkirk but lost much equipment.
Britain, the Atlantic and the Mediterranean
Germany needed air superiority before any credible invasion of Britain. During the Battle of Britain, Fighter Command's radar-supported system survived the Luftwaffe's attacks. The Blitz then brought sustained bombing to British cities, while the larger Battle of the Atlantic threatened the shipping on which Britain depended.
Italy entered the war in June 1940. Fighting spread across North and East Africa, the Mediterranean and the Balkans. British and Commonwealth forces fought Italian and later German armies in the desert, while control of Malta, Egypt and the Suez route had strategic importance.
Operation Barbarossa and the Eastern Front
Germany and its allies invaded the Soviet Union on 22 June 1941. Initial advances captured huge territories and prisoners, but German forces failed to destroy Soviet resistance before winter. The campaign was designed as a racial and colonial war: mass shootings, starvation policy and the murder of Soviet Jews accompanied military operations.
The Soviet victory at Stalingrad in February 1943 followed months of urban fighting and the encirclement of the German Sixth Army. At Kursk later that year, Germany failed to regain the strategic initiative. Soviet offensives then drove west at enormous human cost.
Pearl Harbor and the Pacific War
Japan had been at war in China since 1937. Facing economic pressure and an American oil embargo, its leaders chose to seize territories across Southeast Asia and the Pacific. The attack on Pearl Harbor on 7 December 1941 damaged the US Pacific Fleet but missed its aircraft carriers and did not destroy repair and fuel facilities.
Japan rapidly captured Hong Kong, Malaya, Singapore, the Philippines and the Dutch East Indies. The battles of the Coral Sea and Midway checked further expansion in 1942. American forces then advanced through selected island groups while Allied campaigns continued in New Guinea, Burma and China.
North Africa, Italy and strategic bombing
The British victory at El Alamein and Allied landings in Morocco and Algeria placed Axis forces in North Africa between two armies. They surrendered in Tunisia in May 1943. The Allies invaded Sicily and mainland Italy; Mussolini fell, but German forces occupied much of the country and defended a series of strong positions.
British and American bombers attacked German industry, transport and cities. The offensive diverted German aircraft and guns and damaged production, but area bombing also killed large numbers of civilians. Historians continue to debate the military effectiveness and moral choices of different phases of the campaign.
D-Day and the defeat of Nazi Germany
On 6 June 1944 Allied forces landed in Normandy after an immense deception and logistical effort. The beachhead survived, and the Allies broke out of Normandy in late July. Paris was liberated in August, but an ambitious airborne operation in the Netherlands failed to cross the Rhine and Germany launched a final major western offensive in the Ardennes that winter.
In the east, Operation Bagration destroyed much of Germany's Army Group Centre in summer 1944. Soviet and Western armies entered Germany in 1945. Hitler died in Berlin, and Germany surrendered unconditionally in May.
The defeat of Japan
American submarine warfare and bombing strangled Japanese transport and industry while costly battles brought Allied forces closer to the home islands. US forces captured Iwo Jima and Okinawa in 1945. The Soviet Union declared war on Japan on 8 August and attacked Japanese forces in Manchuria.
The United States dropped atomic bombs on Hiroshima on 6 August and Nagasaki on 9 August, killing tens of thousands immediately and many more later. Japan announced its acceptance of surrender on 15 August and signed the formal instrument on 2 September. Historians debate the relative weight of the atomic bombings, Soviet entry, blockade and Japanese political calculations.
A transformed world
The war ended Axis dictatorship but left destroyed cities, displaced populations and contested borders. The Holocaust and other crimes led to trials and new legal concepts. The United States and Soviet Union emerged as superpowers, European empires weakened and the Cold War began before wartime reconstruction was complete.
Why It Matters
A chronological overview gives readers the framework needed to understand individual battles without mistaking any one campaign for the whole global conflict.