World War II

World War II was the most destructive armed conflict in recorded human history. It involved more than fifty nations and drew soldiers, civilians, industrial capacity, scientific research, and colonial resources from every inhabited continent. The war is conventionally dated from the German invasion of Poland on September 1, 1939 to the formal Japanese surrender aboard the USS Missouri on September 2, 1945, although related conflicts in Asia, including the Second Sino-Japanese War, began earlier.

The war was fought between two principal coalitions. The Axis Powers were led by Nazi Germany, the Kingdom of Italy, and the Empire of Japan. The Allied Powers were led by the United Kingdom, the Soviet Union, the United States, and the Republic of China, joined by dozens of other nations including Canada, Australia, New Zealand, India, South Africa, France and the Free French forces, Brazil, Mexico, and many governments in exile.

Casualty estimates range from roughly 70 to 85 million dead, the majority of them civilians. The Soviet Union and China suffered the highest absolute losses. The Holocaust, the systematic genocide of Europe's Jewish population by Nazi Germany, accounted for approximately six million of those civilian deaths. Bombing campaigns, famine, disease, forced labor, and mass atrocities compounded the toll.

The consequences of the war reshaped the twentieth century. The United States and the Soviet Union emerged as superpowers, European colonial empires began to dissolve, the atomic age began, and the United Nations was founded to coordinate international security and humanitarian action. Many of the political borders, alliances, and institutions that define the modern world trace directly to the years between 1939 and 1945.

The origins of World War II are rooted in the unresolved tensions of the First World War and the interwar decades. The Treaty of Versailles in 1919 imposed heavy reparations and territorial losses on Germany, fueling lasting resentment. The collapse of international finance during the Great Depression destabilized democracies worldwide and undermined confidence in liberal governance. In this climate, authoritarian and fascist movements rose to power in Germany, in the Kingdom of Italy under Benito Mussolini, and in the Empire of Japan, where militarists consolidated control over the government.

The League of Nations, designed to arbitrate international disputes, proved unable to enforce its decisions. Japan invaded Manchuria in 1931 and expanded its war against China in 1937. Italy invaded Ethiopia in 1935. Nazi Germany, under Adolf Hitler, remilitarized the Rhineland in 1936, annexed Austria in 1938, and seized Czechoslovakia in two stages in 1938 and 1939. Each aggression was met with concession or protest rather than collective military response.

In August 1939, Germany and the Soviet Union signed the Molotov-Ribbentrop Pact, a non-aggression agreement that included a secret protocol dividing eastern Europe between them. On September 1, 1939, Germany invaded Poland. Two days later, the United Kingdom and France declared war on Germany, marking the formal beginning of the European war.

The Holocaust was the systematic, state-sponsored persecution and genocide of approximately six million European Jews by Nazi Germany and its collaborators between 1933 and 1945. The campaign of annihilation was pursued through ghettoization, mass shootings by Einsatzgruppen units on the Eastern Front, and industrialized killing at extermination camps including Auschwitz-Birkenau, Treblinka, Sobibor, Belzec, Chelmno, and Majdanek. Concentration camps such as Dachau, Buchenwald, and Bergen-Belsen held political prisoners, forced laborers, and victims of persecution under brutal conditions.

Alongside Jewish victims, Nazi Germany also targeted Roma and Sinti people, Soviet prisoners of war, Polish civilians, disabled people killed under the Aktion T4 program, political prisoners, Jehovah's Witnesses, and LGBTQ+ individuals. The Holocaust is widely studied as the central moral and historical reference point of the war and as the defining case of genocide in modern international law. Because of the depth and distinct character of this subject matter, it is treated in greater detail on its own dedicated page at The Holocaust.

By the spring of 1945, Germany was encircled. Soviet forces advancing from the east and Allied forces advancing from the west converged on Berlin. Adolf Hitler died by suicide in his Berlin bunker on April 30, 1945. German representatives signed an act of unconditional surrender at Reims, France on May 7, followed by a ratification in Berlin on May 8. Across Europe and the Americas, the day is remembered as Victory in Europe Day, or V-E Day.

The war against Japan continued. Conventional and firebombing raids on Japanese cities, the fall of Okinawa after intense fighting, and an Allied naval blockade had brought the Japanese home islands to the edge of collapse. On August 6 and August 9, 1945, the United States dropped atomic bombs on Hiroshima and Nagasaki. On August 8, the Soviet Union declared war on Japan and invaded Manchuria. Emperor Hirohito announced Japan's surrender by radio on August 15. The formal instrument of surrender was signed aboard the USS Missouri in Tokyo Bay on September 2, 1945, ending the Second World War.

The political order that emerged from the war was radically different from the one that had entered it. The United Nations was founded in San Francisco in 1945 to coordinate international security, humanitarian response, and human rights. The Nuremberg Trials prosecuted senior Nazi leaders for crimes against peace, war crimes, and crimes against humanity, establishing principles of individual criminal responsibility in international law. Parallel tribunals in Tokyo judged Japanese leaders on similar charges.

Germany was divided into four occupation zones, which evolved into the Federal Republic of Germany in the west and the German Democratic Republic in the east. The rivalry between the United States and the Soviet Union hardened into the Cold War, shaping global politics for more than four decades. The Marshall Plan financed European reconstruction, the International Monetary Fund and the World Bank were established at the Bretton Woods conference, and NATO was formed in 1949. Decolonization accelerated across Asia and Africa, with India, Indonesia, the Philippines, and dozens of other nations achieving independence in the decades that followed. The State of Israel was established in 1948, in part a response to the Holocaust and to a long-standing Zionist movement.

The Geneva Conventions were revised in 1949 to provide broader protections for civilians, prisoners of war, and the wounded. The Universal Declaration of Human Rights was adopted by the United Nations General Assembly in 1948. Commemoration and memory culture became a defining feature of postwar civic life, with memorials, museums, and national remembrance days now found on every continent. The shadow of World War II continues to shape international institutions, borders, alliances, and public debate into the twenty-first century.

Detailed citations, data references, and institutional sources for all CountryReports content are listed on the Sources page. The following government archives, national museums, and academic institutions are the primary authorities we rely on for World War II content. Each link points to the institution's homepage.

Government Archives and Official Records

• National Archives and Records Administration (NARA) — United States Government records of the war, including operational reports, diplomatic cables, and the holdings of the Records of the War Department.
• The National Archives (United Kingdom) — Cabinet War Room papers, War Office records, and Commonwealth operational history.
• Library of Congress — Official photograph collections, oral histories from the Veterans History Project, and published Government documents.
• Bundesarchiv (German Federal Archives) — German state records relating to the Third Reich, the Wehrmacht, and postwar denazification.
• United Nations Archives and Records Management Section — Founding documents of the United Nations, drafting records of the Universal Declaration of Human Rights, and postwar reconstruction records.

National Museums and Memorial Institutions

• United States Holocaust Memorial Museum — Holocaust research, survivor testimony, and the Encyclopedia of Camps and Ghettos.
• Imperial War Museums (United Kingdom) — British and Commonwealth operational records, oral histories, and the official British war art collection.
• The National WWII Museum (New Orleans) — United States wartime home-front and operational history, including its Research Starters and oral-history archive.
• Yad Vashem — The World Holocaust Remembrance Center — Central Database of Shoah Victims' Names, photo archive, and educational resources.
• Commonwealth War Graves Commission — Register of Commonwealth casualties, cemeteries, and memorials in more than 150 countries.
• American Battle Monuments Commission — United States overseas military cemeteries and memorials, including the Normandy American Cemetery.

Academic Research Centers

• Office of the Historian, United States Department of State — Foreign Relations of the United States series, covering wartime diplomacy.
• Harvard University Davis Center for Russian and Eurasian Studies — Scholarship on the Eastern Front and the Soviet war effort.
• University of Cambridge — Faculty of History — Research and publications on the political, military, and social history of the Second World War.

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