History of World War II

World War II was a global conflict fought from 1939 to 1945 between the Axis powers (primarily Germany, Italy, and Japan) and the Allies (primarily the United Kingdom, the Soviet Union, the United States, China, and their partners). 

Origins and causes

The war’s roots include unresolved tensions from World War I, the harsh terms of the Treaty of Versailles, worldwide economic hardship during the Great Depression, and aggressive expansionist ideologies—particularly Nazism in Germany, Fascism in Italy, and militarism in Japan. 

Major phases and turning points

European opening (1939–1941): Germany invaded Poland on 1 September 1939, which triggered Britain and France to declare war; Germany then used blitzkrieg to conquer much of Western Europe in 1940. 

Battle of Britain and the air war (1940): Britain resisted a sustained German air campaign, preventing invasion.

Barbarossa and the Eastern Front (1941–1944): Germany invaded the Soviet Union in Operation Barbarossa in 1941; fierce battles (Stalingrad, Kursk) and Soviet resilience began pushing German forces back.

Pacific War (1937/1941–1945): Japan’s earlier expansion in East Asia escalated with the 1941 Pearl Harbor attack, bringing the U.S. fully into the war; decisive naval battles like Midway (1942) turned the tide in the Pacific. 

North Africa and Italy (1940–1944): Campaigns in North Africa and the Allied invasion of Sicily/Italy weakened Axis control in the Mediterranean. 

Western Allied advance (1944–1945): The D-Day landings (Normandy, June 1944) opened a Western front; Allied forces advanced into Germany while the Soviets pressed from the east. 

End of the war (May–September 1945): Germany surrendered in May 1945 following the fall of Berlin and Hitler’s suicide; Japan surrendered in September 1945 after the atomic bombings of Hiroshima and Nagasaki and the Soviet entry into the war against Japan. 

Background and timeline

Outbreak and early war: The war began when Germany invaded Poland on September 1, 1939, prompting Britain and France to declare war on Germany.

Global expansion: The conflict spread into Western Europe, North Africa, the Mediterranean, and from 1941 into the Pacific after Japan’s attack on Pearl Harbor, bringing the United States fully into the war.

End and consequences: Fighting ended in Europe in May 1945 and in the Pacific in August 1945; the war caused tens of millions of deaths and triggered decolonization, major shifts in global power, and the creation of the United Nations.