Quick answer: The key World War 2 facts: the war (1939β1945) was the deadliest conflict in history, killing an estimated 70 to 85 million people, about 3% of the world’s population. It began when Germany invaded Poland on 1 September 1939 and ended in Europe on 8 May 1945 and in Asia when Japan formally surrendered on 2 September 1945. The main sides were the Allies (including Britain, the Soviet Union, the United States and China) and the Axis (Germany, Italy and Japan).
World War 2 reshaped borders, technology and international politics for the rest of the 20th century. This guide covers the key facts: why the war started, how it unfolded, the turning points, the human cost, and some surprising facts that are less often told.
World War 2 facts at a glance
| Fact | Detail |
|---|---|
| Dates | 1 September 1939 to 2 September 1945 |
| Main Allied powers | United Kingdom, Soviet Union, United States, China, France |
| Main Axis powers | Germany, Italy, Japan |
| Estimated deaths | About 70 to 85 million, most of them civilians |
| Country with most deaths | Soviet Union, about 27 million |
| Holocaust victims | About 6 million Jews, plus millions of others |
| Military personnel mobilized | More than 100 million |
| Result | Allied victory; the United Nations founded in October 1945 |
What caused World War 2?
- The Treaty of Versailles (1919). After World War 1, Germany lost territory, had its military restricted and was required to pay reparations. Many Germans resented the treaty.
- The Great Depression. The economic collapse after 1929 caused mass unemployment and helped extremist parties gain support.
- The rise of Adolf Hitler. Hitler became Germany’s chancellor in January 1933, built a dictatorship, rearmed Germany and sought territory in Eastern Europe.
- Japanese expansion. Japan invaded Manchuria in 1931 and launched a full-scale war against China in 1937.
- Appeasement. Britain and France allowed Germany to take Austria and, after the 1938 Munich Agreement, part of Czechoslovakia, hoping to avoid war.
- The Nazi-Soviet Pact. In August 1939, Germany and the Soviet Union agreed not to fight each other and secretly divided Eastern Europe, clearing the way to invade Poland.
World War 2 timeline: key events
| Date | Event |
|---|---|
| 1 Sep 1939 | Germany invades Poland |
| 3 Sep 1939 | Britain and France declare war on Germany |
| MayβJun 1940 | Germany conquers France, Belgium and the Netherlands; evacuation from Dunkirk |
| JulβOct 1940 | Battle of Britain: the RAF defeats the German air campaign |
| 22 Jun 1941 | Germany invades the Soviet Union (Operation Barbarossa) |
| 7 Dec 1941 | Japan attacks Pearl Harbor; the US enters the war |
| Jun 1942 | Battle of Midway: turning point in the Pacific |
| Aug 1942βFeb 1943 | Battle of Stalingrad: German army destroyed |
| 6 Jun 1944 | D-Day: Allied landings in Normandy |
| 30 Apr 1945 | Hitler dies by suicide in Berlin |
| 8 May 1945 | Victory in Europe (VE) Day |
| 6 and 9 Aug 1945 | Atomic bombs dropped on Hiroshima and Nagasaki |
| 2 Sep 1945 | Japan formally surrenders aboard USS Missouri |
The turning points of World War 2
Battle of Britain (1940)
Germany needed control of the air to invade Britain. The Royal Air Force, helped by radar, held it off. It was Hitler’s first major defeat.
Battle of Midway (1942)
Just six months after Pearl Harbor, US forces, helped by codebreakers who had cracked Japanese naval codes, sank four Japanese aircraft carriers. Japan was on the defensive from then on.
Battle of Stalingrad (1942β1943)
One of the bloodiest battles in history, with total casualties estimated at around 2 million. The surrender of the German Sixth Army in February 1943 marked the start of the Soviet advance toward Berlin.
D-Day (1944)
On 6 June 1944, about 156,000 Allied troops landed on five beaches in Normandy, the largest seaborne invasion in history. It opened a western front that, together with the Soviet advance from the east, defeated Germany within a year.
Technology that changed during the war
- Radar became essential for detecting aircraft and ships.
- Codebreaking and early computers. Polish mathematicians first broke the German Enigma machine in the 1930s. Their work was expanded at Britain’s Bletchley Park, where the Colossus computers were also built to break other German codes.
- Jet aircraft. Germany’s Messerschmitt Me 262 was the first operational jet fighter.
- Rockets. Germany’s V-2 became the first human-made object to reach space in 1944. Its technology later shaped the space race.
- Penicillin. Mass production of the antibiotic began during the war and saved many wounded soldiers (see curious inventions that changed the world).
- Nuclear weapons. The US Manhattan Project produced the first atomic bombs.
Surprising World War 2 facts
- Navajo code talkers created an unbroken code. US Marines used the Navajo language to send messages in the Pacific, and Japan never cracked it.
- A Japanese soldier kept fighting until 1974. Hiroo Onoda remained in the Philippine jungle for nearly 29 years because he didn’t believe the war was over. He surrendered only when his former commander came to order him to.
- Britain used fake armies. Before D-Day, Operation Fortitude used inflatable tanks, fake radio traffic and double agents to convince Germany the invasion would land at Calais.
- A bear served in the Polish army. Wojtek, a Syrian brown bear adopted by Polish soldiers, helped carry ammunition crates at the Battle of Monte Cassino.
- Most deaths were civilians. Bombing, massacres, famine, disease and genocide killed far more civilians than soldiers.
The legacy of World War 2
- The United Nations was founded in 1945 to prevent future world wars.
- The Nuremberg trials established that leaders can be tried for crimes against humanity.
- Europe was divided between Western democracies and Soviet-controlled states, starting the Cold War.
- Many colonies in Asia and Africa gained independence in the following decades.
Frequently asked questions
When did World War 2 start and end?
It started on 1 September 1939 with Germany’s invasion of Poland and ended on 2 September 1945, when Japan formally surrendered.
Who won World War 2?
The Allies won, led by the United Kingdom, the Soviet Union, the United States and China.
How many people died in World War 2?
Estimates range from about 70 to 85 million, including soldiers and civilians, making it the deadliest war in history.
Why did the US join World War 2?
The US entered the war after Japan attacked Pearl Harbor, Hawaii, on 7 December 1941. Germany and Italy declared war on the US a few days later.
What was the main cause of World War 2?
Historians point to several causes together: the Treaty of Versailles, the Great Depression, the aggressive expansion of Nazi Germany, Fascist Italy and Imperial Japan, and the failure of appeasement.
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Sources
- The National WWII Museum, New Orleans: “Research Starters: Worldwide Deaths in World War II”. nationalww2museum.org
- Imperial War Museums (UK). iwm.org.uk
- United States Holocaust Memorial Museum: Holocaust Encyclopedia. encyclopedia.ushmm.org
- US National Archives: World War II records. archives.gov
- Encyclopaedia Britannica: “World War II”.