World War II, also known as the Second World War, was the largest and deadliest conflict in human history, involving more than 50 nations. The war was fought on land, sea, and air in nearly every part of the globe. The war began following the invasion of Poland by Nazi Germany in 1939. It continued until 1945 when Japan surrendered to the United States after atomic bombs were dropped on Hiroshima and Nagasaki. An estimated 60 to 80 million people had died, including up to 55 million civilians, and numerous cities in Europe and Asia were reduced to rubble by the end of the war.
Origins of World War II
The origins of World War II can be traced back to the unresolved issues following World War I. The economic crisis of the Great Depression and the rise of fascism in Europe, particularly in Germany and Italy, contributed to the growing tensions that eventually led to the outbreak of the war. Adolf Hitler and his National Socialist German Workers’ Party, also known as the Nazi Party, rose to power in Germany, fueled by the country’s economic instability and lingering resentment over the harsh terms imposed by the Treaty of Versailles.
The rise of Hitler and the Nazi Party
As early as 1923, Adolf Hitler had predicted a general European war that would result in “the extermination of the Jewish race in Germany” in his memoir and propaganda tract “Mein Kampf.” Hitler swiftly consolidated power after becoming Chancellor of Germany in 1933. He anointed himself Führer (supreme leader) in 1934. He was obsessed with the idea of the superiority of the “pure” German race, which he called “Aryan,” and believed that war was the only way to gain the necessary “Lebensraum,” or living space, for the German race to expand. In the mid-1930s, he secretly began the rearmament of Germany, violating the Versailles Treaty.
Growing tensions and aggression in Europe
Hitler invaded Austria in 1938 and annexed Czechoslovakia the following year after signing alliances with Italy and Japan. Due to internal politics, the United States and the Soviet Union did not react to Hitler’s open aggression, and neither France nor Britain (the other two nations most affected by the Great War) were eager to confront him.
Outbreak of World War II (1939)
In late August 1939, Hitler and Soviet leader Joseph Stalin signed the German-Soviet Nonaggression Pact, causing powers in London and Paris to worry. Hitler had been planning an invasion of Poland for a while. It was a nation that Great Britain and France had pledged military support should Germany attack it. By signing the pact with Stalin, Hitler would not have to fight on two fronts once he invaded Poland and would have Soviet assistance in conquering and dividing it. On 1 September 1939, Hitler invaded Poland from the west; two days later, France and Britain declared war on Germany, beginning World War II.
The phoney war and naval warfare
On 17 September, Soviet troops invaded Poland from the east. Under attack from both sides, Poland fell quickly, and by early 1940 Germany and the Soviet Union had divided control over the nation, according to a secret protocol appended to the Nonaggression Pact. Stalin’s forces then moved to occupy the Baltic States (Estonia, Latvia, and Lithuania) and defeated a resistance in Finland in the Russo-Finnish War.
During the six months following the invasion of Poland, the lack of action on the part of Germany and the Allies in the West led to talk in the news media of a “phoney war.” At sea, however, the British and German navies faced off in heated battle, and lethal German U-boat submarines struck at merchant shipping bound for Britain, sinking more than 100 vessels in the first four months of World War II.
World War II in the West (1940-41)
On 9 April 1940, Germany simultaneously invaded Norway and occupied Denmark, and the war began in earnest. On 10 May, German forces swept through Belgium and the Netherlands in what became known as “blitzkrieg,” or lightning war. Three days later, Hitler’s troops crossed the Meuse River and struck French forces at Sedan, located at the northern end of the Maginot Line, a complex chain of fortifications constructed after World War I and regarded as an impenetrable defensive barrier. The Germans broke through the line with their tanks and planes and continued to the rear, effectively making it useless.
The fall of France and the Battle of Britain
The British Expeditionary Force (BEF) was evacuated by sea from Dunkirk in late May, while French forces mounted a doomed resistance in the south. With France on the verge of collapse, Italy’s fascist dictator Benito Mussolini allied with Hitler, the Pact of Steel, and Italy declared war against France and Britain on 10 June.
On 14 June, German forces entered Paris; a new government formed by Marshal Philippe Pétain (France’s hero of World War I) requested an armistice two nights later. France was subsequently divided into two zones, one under German military occupation and the other under Pétain’s government, installed at Vichy France. Hitler now turned his attention to Britain, which had the defensive advantage of being separated from the Continent by the English Channel.
To pave the way for an amphibious invasion (Operation Sea Lion), German planes extensively bombed Britain from September 1940 until May 1941, known as the Blitz, including night raids on London and other industrial centres that caused heavy civilian casualties and damage. The Royal Air Force (RAF) eventually defeated the Luftwaffe (German Air Force) in the Battle of Britain, and Hitler postponed his plans to invade. With Britain’s defensive resources pushed to the limit, Prime Minister Winston Churchill began receiving crucial aid from the United States under the Lend-Lease Act, passed by Congress in early 1941.
Hitler vs. Stalin: Operation Barbarossa (1941-42)
By early 1941, Hungary, Romania, and Bulgaria had joined the Axis, and German troops overran Yugoslavia and Greece in April. Hitler’s conquest of the Balkans was a precursor for his fundamental objective: an invasion of the Soviet Union, whose vast territory would give the German master race the “Lebensraum” it needed. The other half of Hitler’s strategy was exterminating Jews throughout German-occupied Europe. Plans for the “Final Solution” were introduced around the time of the Soviet offensive, and over the next three years, more than 4 million Jews would perish in the death camps established in occupied Poland.
On 22 June 1941, Hitler ordered the invasion of the Soviet Union, codenamed Operation Barbarossa. Though Soviet tanks and aircraft greatly outnumbered the Germans, Russian aviation technology was largely obsolete, and the impact of the surprise invasion helped Germans get within 200 miles of Moscow by mid-July. Arguments between Hitler and his commanders delayed the next German advance until October. A Soviet counteroffensive and the onset of harsh winter weather then stalled it.
World War II in the Pacific (1941-43)
With Britain facing Germany in Europe, the United States was the only nation capable of combating Japanese aggression, which by late 1941 included an expansion of its ongoing war with China and the seizure of European colonial holdings in the Far East. On 7 December 1941, 360 Japanese aircraft attacked the US naval base at Pearl Harbor in Hawaii, taking the Americans completely by surprise and claiming the lives of more than 2,300 troops. The attack on Pearl Harbor served to unify American public opinion in favour of entering World War II. On 8 December, the United States declared war on Japan. Germany and its allies promptly declared war on the United States.
Turning point: The Battle of Midway
After a long string of Japanese victories, the US Pacific Fleet won the Battle of Midway in June 1942, which proved to be a turning point in the war. On Guadalcanal, one of the southern Solomon Islands, the Allies also succeeded against Japanese forces in a series of battles from August 1942 to February 1943, helping turn the tide further in the Pacific. In mid-1943, Allied naval forces began an aggressive counterattack against Japan, involving a series of amphibious assaults on key Japanese-held islands in the Pacific. This “island-hopping” strategy proved successful, and Allied forces moved closer to their ultimate goal of invading mainland Japan.
Toward Allied victory in World War II (1943-45)
British and American forces defeated the Italians and Germans in North Africa by 1943. An Allied invasion of Sicily and Italy followed, and Mussolini’s government fell in July 1943, though Allied fighting against the Germans in Italy would continue until 1945.
The Eastern Front: Soviet victory at Stalingrad
On the Eastern Front, a Soviet counteroffensive launched in November 1942 ended the bloody Battle of Stalingrad, which had seen some of the fiercest combat of World War II. The approach of winter, along with dwindling food and medical supplies, spelt the end for German troops there, and the last of them surrendered on 31 January 1943.
D-Day and the liberation of Europe
The Allies began their invasion of Europe on 6 June 1944, landing 156,000 British, Canadian, and American soldiers on the beaches of Normandy, France. As a result, Hitler sent all his remaining forces into Western Europe, ensuring Germany’s defeat in the east. The Soviets advanced into Poland, Czechoslovakia, Hungary, and Romania, while Hitler gathered his forces to drive the Americans and British back from Germany in the Battle of the Bulge (December 1944-January 1945).
The fall of Berlin and Hitler’s death
By the time Germany formally surrendered on 8 May 1945, Soviet forces had occupied much of the country following an intense aerial bombardment in February 1945. Hitler had already committed suicide in his Berlin bunker on 30 April.
World War II ends (1945)
At the Potsdam Conference of July-August 1945, British Prime Minister Winston Churchill, US President Harry S. Truman, and Soviet leader Joseph Stalin discussed the ongoing war with Japan and the peace settlement with Germany. Post-war Germany would be divided into four occupation zones controlled by the Soviet Union, Britain, the United States, and France.
The atomic bomb and Japan’s surrender
Heavy casualties were sustained in the campaigns at Iwo Jima (February 1945) and Okinawa (April-June 1945), and fears of the even costlier land invasion of Japan led Truman to authorise the use of a new and devastating weapon—the atomic bomb. On 6 August 1945, the US dropped the first atomic bomb on the Japanese city of Hiroshima, followed by a second bomb on Nagasaki on 9 August.
Faced with an imminent invasion of the Japanese archipelago, the possibility of additional atomic bombings, and the Soviet Union’s declared entry into the war against Japan on the eve of invading Manchuria, Japan announced on 10 August its intention to surrender, signing a surrender document on 2 September 1945.
The legacy of World War II
During the war, the Nazis killed six million Jews (an event known as the holocaust) and persecuted and murdered millions of Black people and others they deemed inferior. This included Romani people, ethnic Poles, Soviet prisoners of war, and physically and mentally disabled people.
War II changed the global political alignment and social structure and set the foundation for the international order of the world’s nations for the rest of the 20th century and into the present day. The United Nations was established to foster international cooperation and prevent future conflicts, with the victorious great powers—China, France, the Soviet Union, the United Kingdom, and the United States—becoming the permanent members of its Security Council.
The Soviet Union and the United States emerged as rival superpowers, setting the stage for the nearly half-century-long Cold War. In the wake of European devastation, the influence of its great powers waned, triggering the decolonisation of Africa and Asia. Most countries whose industries had been damaged moved towards economic recovery and expansion. Political and economic integration, especially in Europe, began as an effort to forestall future hostilities, end pre-war enmities, and forge a sense of shared identity.