## TL;DR
World War II reshaped the global order — ending European colonial empires, establishing US-Soviet superpowers, creating the United Nations, and setting the stage for the Cold War.

## Core Explanation
Causes: punitive Treaty of Versailles, Great Depression radicalization, fascist expansionism, appeasement failure. The war began with Germany's invasion of Poland (September 1, 1939).

## Detailed Analysis
The Pacific War (1941-1945) was defined by naval aviation and island-hopping. The Manhattan Project developed atomic weapons — Hiroshima and Nagasaki forced Japan's surrender. Yalta and Potsdam divided Europe into Western and Soviet spheres.

## Further Reading
- Imperial War Museum WWII Collections
- US Holocaust Memorial Museum
- National WWII Museum (New Orleans)