Global conflict, 1939-1945
World War II
World War II was the largest war in history, fought across Europe, Africa, Asia, and the Pacific, reshaping borders, societies, technology, and the global balance of power.
How it began
The war in Europe began when Nazi Germany invaded Poland on September 1, 1939. Britain and France declared war two days later. The conflict grew from unresolved tensions after World War I, aggressive expansion by fascist states, economic crisis, militarism, and failures of international diplomacy. In Asia, Japan had already been expanding through war in China before the European conflict began.
The Axis powers
The main Axis powers were Germany, Italy, and Japan. Each pursued expansion, but their goals and theaters differed. Nazi Germany sought domination in Europe and carried out a genocidal racial empire. Fascist Italy sought influence around the Mediterranean and Africa. Imperial Japan expanded across East Asia and the Pacific, building a military empire based on resource control and regional dominance.
The Allied powers
The Allies included Britain, the Soviet Union, the United States, China, France, and many other nations and resistance movements. Their cooperation was often tense because their political systems and postwar aims differed sharply. Still, the scale of Axis aggression forced coordination in military production, intelligence, logistics, and strategy. The alliance became one of the decisive features of the war.
How it became global
Germany conquered or occupied much of Europe, while Italy fought in the Mediterranean and North Africa. Japan's expansion in Asia and the Pacific brought the United States fully into the war after the attack on Pearl Harbor on December 7, 1941. By then, the conflict linked multiple regional wars into one worldwide struggle, with battles at sea, in deserts, in cities, in jungles, and across enormous supply lines.
The Holocaust and occupation
The Holocaust was the systematic murder of six million Jews by Nazi Germany and its collaborators, along with the persecution and killing of Roma people, disabled people, Poles, Soviet prisoners of war, political opponents, LGBTQ people, and others targeted by Nazi ideology. Occupied Europe also saw forced labor, mass reprisals, deportations, resistance movements, and daily survival under brutal rule.
War production and technology
World War II was a war of factories as much as armies. Aircraft, tanks, ships, radar, codebreaking machines, antibiotics, synthetic materials, and logistical systems shaped outcomes. The Manhattan Project produced atomic bombs, which the United States used against Hiroshima and Nagasaki in August 1945. Technology did not replace strategy or manpower, but it changed the speed, scale, and destructive power of war.
Why it matters
World War II transformed the twentieth century. It ended the Nazi regime, exposed the full horror of the Holocaust, accelerated decolonization, led to the creation of the United Nations, and left the United States and Soviet Union as rival superpowers. Its consequences shaped borders, memory, law, science, military planning, and international politics for generations.