World War II

[ Show/Hide ] Overview Course Causes · Timeline · Theaters of war Participants Allies · Axis powers Casualties Casualties · The Holocaust · War crimes European Theater 1939–1940 Invasion of Poland · Winter War · Phoney War · Invasion of Norway and Denmark · Battle of France · Dunkirk evacuation · Battle of Britain · The Blitz 1941–1942 Balkans campaign · Operation Barbarossa · Siege of Leningrad · Battle of Moscow · Battle of Stalingrad 1943–1945 Battle of Kursk · Allied invasion of Sicily · Allied invasion of Italy · D-Day (Normandy landings) · Operation Bagration · Battle of the Bulge · Battle of Berlin · V-E Day Pacific Theater 1937–1942 Second Sino-Japanese War · Attack on Pearl Harbor · Wake Island · Fall of Singapore · Coral Sea · Battle of Midway 1942–1945 Guadalcanal · Burma campaign · Philippine Sea · Leyte Gulf · Iwo Jima · Okinawa · Atomic bombings · Surrender of Japan Other Theaters Africa & Med. North African campaign · El Alamein · Operation Torch · Battle of the Atlantic · Mediterranean Key Figures Allied leaders Franklin D. Roosevelt · Harry S. Truman · Winston Churchill · Joseph Stalin · Charles de Gaulle · Chiang Kai-shek Axis leaders Adolf Hitler · Benito Mussolini · Hideki Tojo · Emperor Hirohito Commanders Dwight D. Eisenhower · Douglas MacArthur · George S. Patton · Bernard Montgomery · Georgy Zhukov · Erwin Rommel · Isoroku Yamamoto Aftermath Postwar Aftermath of World War II · United Nations · Nuremberg Trials · Tokyo Trials · Cold War · Marshall Plan · Decolonization · Division of Germany · Occupation of Japan

World War II (also called the Second World War) was a global conflict fought from September 1, 1939, to September 2, 1945. It pitted two major alliances against each other: the Allies (led by the United Kingdom, the Soviet Union, the United States, and China) and the Axis powers (led by Nazi Germany, Fascist Italy, and the Empire of Japan). Nearly every country in the world was involved in some way, and many nations committed all of their resources in pursuit of total war.

World War II is the deadliest conflict in human history. Between 70 and 85 million people died, more than half of them civilians. Millions were killed in genocides, including the Holocaust, in which Nazi Germany systematically murdered around six million Jews along with millions of others. The war also saw the first and only use of nuclear weapons in combat, when the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki in August 1945.

The war's causes stretched back to the aftermath of World War I. The harsh terms of the Treaty of Versailles left Germany bitter and economically struggling. The rise of fascism in Europe and militarism in Japan pushed the world toward another conflict. Key events leading up to the war included Japan's invasion of Manchuria in 1931, the Spanish Civil War (1936–1939), the Second Sino-Japanese War starting in 1937, and Germany's annexation of Austria and the Sudetenland in 1938.

After the Allied victory, the United Nations was created to promote international cooperation and prevent future wars. The Soviet Union and the United States emerged as rival superpowers, setting the stage for the decades-long Cold War. European colonial empires weakened, triggering decolonization across Africa and Asia. The war fundamentally reshaped the political, economic, and social structures of the entire world.

World War I (1914–1918) had dramatically reshaped Europe. The defeated Central Powers — including Germany, Austria-Hungary, Bulgaria, and the Ottoman Empire — lost territory and influence. New nations like Poland, Czechoslovakia, and Yugoslavia were carved out of the old empires. The Russian Empire collapsed into revolution and became the Soviet Union.

To prevent another world war, the League of Nations was established in 1920 through the Paris Peace Conference. Its goals were to settle disputes through negotiation and to promote disarmament. However, the League lacked enforcement power and would prove unable to stop aggression in the 1930s.

The Treaty of Versailles (1919) punished Germany severely. Germany lost about 13 percent of its European territory and all of its overseas colonies. It was forced to pay heavy reparations (financial penalties) to the Allies and had strict limits placed on the size of its military. These terms created deep resentment among many Germans.

During the Great Depression of the 1930s, economic hardship and political instability pushed people toward extreme political movements. In Germany, Adolf Hitler and the Nazi Party rose to power, promising to undo the Versailles Treaty and restore German greatness. Hitler became chancellor in 1933 and quickly established a totalitarian state (a government with total control over public and private life). He promoted a racist ideology centered on the supposed superiority of an "Aryan" race, and he targeted Jews, Slavic peoples, and other groups as enemies.

In Italy, the fascist movement under Benito Mussolini had already seized power in the 1920s. Mussolini promised to make Italy a great power and pursued aggressive expansion, including the invasion of Ethiopia in 1935.

In Japan, the military gained increasing control over the government during the 1930s. Japan sought to dominate East Asia and began expanding aggressively, starting with the invasion of Manchuria in 1931, where it set up the puppet state of Manchukuo.

Throughout the mid-1930s, the aggressive moves by Germany, Italy, and Japan met with weak responses from other major powers — a policy known as appeasement. When Germany remilitarized the Rhineland in 1936, breaking the Versailles Treaty, Britain and France did nothing. When Italy invaded Ethiopia, the League of Nations imposed limited sanctions that had little effect.

Hitler and Mussolini supported the Nationalist rebels in the Spanish Civil War (1936–1939), using it as a testing ground for their weapons and tactics. The Soviet Union supported the opposing Republican government. The Nationalists won, and Spain under dictator Francisco Franco remained officially neutral during World War II but generally favored the Axis.

In July 1937, Japan launched a full-scale invasion of China, capturing major cities including Beijing, Shanghai, and the capital Nanjing. After the fall of Nanjing, Japanese forces committed the Nanjing Massacre, killing tens or hundreds of thousands of Chinese civilians.

In March 1938, Germany annexed Austria (the Anschluss) with almost no resistance. Then, at the Munich Agreement in September 1938, Britain and France agreed to let Germany take the Sudetenland (the German-speaking part of Czechoslovakia) in exchange for Hitler's promise that he would seek no more territory. British Prime Minister Neville Chamberlain famously declared this would bring "peace for our time." It did not. In March 1939, Germany seized the rest of Czechoslovakia.

Alarmed at last, Britain and France pledged to defend Poland if it were attacked. On August 23, 1939, Germany and the Soviet Union stunned the world by signing the Molotov–Ribbentrop Pact, a non-aggression agreement. Secretly, the pact divided Eastern Europe into German and Soviet "spheres of influence" (areas each power would control).

On September 1, 1939, Germany invaded Poland, using a new tactic called blitzkrieg ("lightning war") — fast-moving coordinated attacks using tanks, infantry, and air power. Britain and France declared war on Germany on September 3, but they provided little direct military help to Poland.

On September 17, the Soviet Union invaded Poland from the east, as secretly agreed in the Molotov–Ribbentrop Pact. Poland was divided between Germany and the Soviet Union by the end of the month. Despite its military defeat, Poland never formally surrendered. A Polish government-in-exile was formed, and many Polish soldiers escaped to continue fighting with the Allies.

What followed in Western Europe was the so-called "Phoney War" — months of declared war with almost no actual fighting between Germany and the Western Allies. During this time, the Soviet Union invaded Finland in November 1939 (the Winter War), and the Soviets forced the Baltic states (Estonia, Latvia, Lithuania) to accept Soviet military bases.

In April 1940, Germany invaded Denmark and Norway to secure supply routes for Swedish iron ore. Then, on May 10, 1940, Germany launched its massive assault westward, invading Belgium, the Netherlands, Luxembourg, and France. Using blitzkrieg tactics and a surprise attack through the Ardennes forest (which the French thought was impassable for tanks), Germany bypassed France's heavily fortified Maginot Line.

The British Expeditionary Force and portions of the French army were pushed to the coast at Dunkirk, where over 300,000 Allied soldiers were evacuated across the English Channel in a dramatic rescue operation. France fell in June 1940, and was divided into German-occupied zones and the collaborationist Vichy France government in the south.

Italy declared war on France and Britain on June 10, 1940, hoping to gain territory from France's collapse.

With France defeated, Britain stood virtually alone against Germany. Hitler planned an invasion of Britain (Operation Sea Lion), but first needed to gain control of the skies. The Battle of Britain (July–October 1940) was a fierce air campaign between the German Luftwaffe and the British Royal Air Force (RAF). The RAF successfully defended British airspace, and Hitler called off the invasion plans.

Germany then shifted to nighttime bombing raids on British cities, known as the Blitz, killing tens of thousands of civilians. Meanwhile, the Battle of the Atlantic raged at sea, as German U-boats (submarines) tried to cut off Britain's supply lines by sinking merchant ships.

In September 1940, Italy invaded British-held Egypt from its colony in Libya, starting the North African campaign. Italy also invaded Greece in October 1940 but was pushed back into Albania. Germany intervened in early 1941, conquering Yugoslavia, Greece, and the island of Crete by May. In North Africa, German General Erwin Rommel (nicknamed "the Desert Fox") led combined German-Italian forces that pushed the British back toward Egypt.

On June 22, 1941, Germany launched Operation Barbarossa, the invasion of the Soviet Union. It was the largest land invasion in history, involving over three million German and Axis soldiers. The attack opened the massive Eastern Front, which would become the deadliest theater of the entire war.

The Axis forces made rapid gains during the summer, capturing vast stretches of Ukraine and the Baltic states and inflicting enormous casualties on the Red Army. However, as winter set in, the German advance stalled just outside Moscow. The Soviets launched a counterattack in December 1941, pushing the Germans back. The failure to capture Moscow marked the end of Germany's blitzkrieg strategy — the war in the east would become a long, grinding struggle.

Meanwhile, tensions had been rising between Japan and the Western powers. Japan's occupation of French Indochina led the United States, Britain, and the Netherlands to impose an oil embargo (a ban on selling oil to Japan), which threatened Japan's ability to fuel its military.

On December 7, 1941, Japan attacked the American naval base at Pearl Harbor in Hawaii, destroying much of the U.S. Pacific Fleet. Simultaneously, Japan attacked British and American territories across Southeast Asia and the Pacific, including the Philippines, Malaya, Hong Kong, and Wake Island.

The United States declared war on Japan on December 8, and Germany and Italy declared war on the United States on December 11. America's entry transformed the war into a truly global conflict. The U.S. and Britain agreed on a "Europe First" strategy — defeating Germany would be the top priority, while fighting a holding action against Japan.

By mid-1942, Japan had conquered a vast empire stretching from Burma to the Dutch East Indies to the western Pacific islands.

Three major turning points shifted the war in the Allies' favor:

The Battle of Midway (June 1942): In the Pacific, the U.S. Navy ambushed a Japanese fleet near Midway Island, sinking four Japanese aircraft carriers. This decisive victory halted Japan's naval expansion and gave the U.S. the initiative in the Pacific.

The Battle of Stalingrad (August 1942 – February 1943): On the Eastern Front, Germany pushed deep into southern Russia, aiming to capture the oil fields of the Caucasus. The German Sixth Army became locked in brutal street-by-street fighting in the city of Stalingrad (now Volgograd). In November 1942, the Soviets launched a massive counterattack that encircled the German forces. After months of starvation and combat, the remaining German troops surrendered in February 1943. Stalingrad was one of the bloodiest battles in history and is widely considered the turning point of the war in Europe.

El Alamein and North Africa (October 1942 – May 1943): In Egypt, British forces under General Bernard Montgomery defeated Rommel's Afrika Korps at the Second Battle of El Alamein in October–November 1942. Combined with the Anglo-American landings in French North Africa (Operation Torch) in November 1942, this led to the complete Axis defeat in North Africa by May 1943.

With North Africa secured, the Allies invaded Sicily in July 1943. The invasion triggered the overthrow of Mussolini, and Italy signed an armistice (ceasefire agreement) with the Allies in September 1943. However, Germany quickly occupied most of Italy, rescued Mussolini, and set up a puppet state in the north called the Italian Social Republic. The Allies fought their way slowly up the Italian peninsula against strong German defenses.

After Stalingrad, the initiative on the Eastern Front shifted permanently to the Soviet Union. In July 1943, Germany attempted one last major offensive at the Battle of Kursk, the largest tank battle in history. The well-prepared Soviet defenses held, and the counterattack that followed began a relentless Soviet advance westward that would continue until the war's end.

On June 6, 1944 — known as D-Day — the Allies launched Operation Overlord, the largest amphibious (sea-to-land) invasion in history. Over 150,000 Allied soldiers landed on the beaches of Normandy, France. Despite heavy casualties, the invasion succeeded, and the Allies established a foothold in Western Europe.

Paris was liberated in August 1944, and Allied forces pushed eastward toward Germany. In December 1944, Germany launched a last-ditch counteroffensive in the Ardennes forest in Belgium, known as the Battle of the Bulge. It was the largest battle the U.S. Army fought in the war, but after initial German success, the Allies pushed them back.

On the Eastern Front, the Soviets launched a massive summer offensive in June 1944 called Operation Bagration, which destroyed the German Army Group Center and liberated Belarus. By early 1945, Soviet forces had pushed into Poland, Romania, Bulgaria, Hungary, and were closing in on Germany itself.

By spring 1945, Allied forces were closing in from both east and west. The Western Allies crossed the Rhine River in March 1945. The Soviets launched their final assault on Berlin in April. On April 30, 1945, with Soviet troops just blocks from his underground bunker, Adolf Hitler committed suicide. Germany surrendered unconditionally on May 7–8, 1945, a date celebrated as V-E Day (Victory in Europe Day).

While the war in Europe raged, the Allies had been steadily pushing back Japan in the Pacific using an "island hopping" strategy — capturing key islands and bypassing others to get closer to Japan.

Major Pacific battles included Guadalcanal (1942–1943), the reconquest of the Philippines (1944–1945), Iwo Jima (February–March 1945), and Okinawa (April–June 1945). Japanese resistance was fierce, with many soldiers fighting to the death and kamikaze pilots deliberately crashing their planes into Allied ships.

By mid-1945, massive Allied bombing raids had devastated Japanese cities, and a naval blockade had cut off Japan's imports. Still, Japan refused to surrender unconditionally.

On August 6, 1945, the United States dropped an atomic bomb called "Little Boy" on Hiroshima, killing an estimated 80,000 people instantly (with tens of thousands more dying later from radiation). On August 9, a second bomb called "Fat Man" was dropped on Nagasaki, killing around 40,000 people instantly.

On August 8, the Soviet Union declared war on Japan and invaded Japanese-held Manchuria, quickly defeating the Japanese forces there.

Faced with the atomic bombs, the Soviet invasion, and the prospect of further destruction, Emperor Hirohito of Japan announced the country's surrender on August 15, 1945 (V-J Day). The formal surrender documents were signed on September 2, 1945, aboard the USS Missouri in Tokyo Bay, officially ending World War II.

The Holocaust was the systematic, state-sponsored murder of approximately six million Jews by Nazi Germany and its collaborators. The Nazis also targeted Roma people, Slavic peoples, disabled people, homosexuals, political opponents, and others — bringing the total number of victims to 11 to 17 million.

The killing was carried out through mass shootings, forced labor, starvation, and extermination camps such as Auschwitz, Treblinka, and Sobibor, where victims were murdered in gas chambers on an industrial scale.

Japan committed widespread atrocities in occupied territories, including the Nanjing Massacre, the use of comfort women (forced sex slaves), brutal treatment of prisoners of war, and medical experiments on prisoners (notably at Unit 731).

The Soviet Union also committed atrocities, including the Katyn massacre (the killing of thousands of Polish officers) and mass deportations of ethnic groups.

After the war, German leaders were tried for war crimes at the Nuremberg Trials, and Japanese leaders faced the International Military Tribunal for the Far East in Tokyo.

World War II fundamentally reshaped the world order. The United Nations was established on October 24, 1945, to promote international cooperation and prevent future wars. The five major Allied powers — the United States, the Soviet Union, the United Kingdom, France, and China — became the permanent members of the UN Security Council, each with veto power.

Germany was divided into four occupation zones controlled by the U.S., Britain, France, and the Soviet Union. This division eventually led to the creation of two separate countries: West Germany (aligned with the Western democracies) and East Germany (a Soviet-backed communist state). They would not reunify until 1990.

Japan was occupied by American forces under General Douglas MacArthur. A new democratic constitution was adopted, and Japan renounced war as a means of settling international disputes.

The wartime alliance between the Western powers and the Soviet Union quickly broke down. The United States and the Soviet Union emerged as rival superpowers with opposing ideologies — capitalism and democracy versus communism. This rivalry, known as the Cold War, dominated global politics for nearly half a century (1947–1991) and led to the formation of the U.S.-led NATO and the Soviet-led Warsaw Pact.

The war weakened European colonial powers, accelerating the process of decolonization. In the decades following the war, dozens of countries in Africa, Asia, and the Middle East gained independence from European rule. In some cases this happened peacefully; in others, like in Algeria and Vietnam, it involved bitter wars of independence.

The United States, which emerged from the war with its homeland largely undamaged, became the world's dominant economic power. Through the Marshall Plan (1948–1952), the U.S. provided about $13 billion (around $170 billion in today's dollars) to help rebuild Western Europe. Japan and West Germany also experienced remarkable economic recoveries in the postwar decades.

The war involved many influential leaders on both sides:

Allied leaders: Franklin D. Roosevelt and later Harry S. Truman (United States), Winston Churchill (United Kingdom), Joseph Stalin (Soviet Union), Charles de Gaulle (Free France), Chiang Kai-shek (China)

Axis leaders: Adolf Hitler (Nazi Germany), Benito Mussolini (Fascist Italy), Hideki Tojo and Emperor Hirohito (Japan)

Military commanders: Dwight D. Eisenhower, Douglas MacArthur, George S. Patton (U.S.); Bernard Montgomery (UK); Georgy Zhukov (Soviet Union); Erwin Rommel (Germany); Isoroku Yamamoto (Japan)

The scale of World War II was unprecedented:

Deaths: 70–85 million total (including about 50 million civilians)

Duration: 6 years (1939–1945 in Europe; related fighting in Asia from 1937)

Countries involved: Over 30 nations formally at war; nearly every country affected

Cost: The U.S. alone spent an estimated $296 billion (1945 dollars) — about $4.9 trillion in today's money

The Soviet Union suffered the most casualties of any nation, losing approximately 27 million people — roughly one in seven of its entire population.