Definition
World War II was a global conflict fought from 1939 to 1945 between the Allied powers — chiefly the United Kingdom, the Soviet Union, the United States, and China — and the Axis powers of Nazi Germany, Imperial Japan, and Fascist Italy. It began with Germany's invasion of Poland and ended with the unconditional surrender of Germany and Japan.
It is the deadliest conflict in recorded history, killing an estimated 70 to 85 million people, the majority of them civilians. The war was fought across Europe, North Africa, the Atlantic and Pacific oceans, and much of Asia, drawing in dozens of nations and tens of millions of soldiers.
Why it matters
How it works
The European war turned on Germany's early conquests, the failed invasion of the Soviet Union, and the eventual Allied counter-offensives from east and west that converged on Berlin in 1945. The Pacific war hinged on Japan's expansion across Asia and the long American island-hopping campaign back toward the Japanese home islands.
Industrial capacity, intelligence, and logistics proved decisive. The Allies out-produced and ultimately encircled the Axis. Germany surrendered in May 1945, and Japan surrendered that August after the atomic bombings, ending the war.