World War I was a global conflict involving major powers divided into Allied and Central Powers. U.S. involvement in World War I reasons included German submarine warfare, economic ties with Britain, and the Zimmermann Telegram. The war introduced new warfare strategies and ended with significant geopolitical changes.
- Key players: Allied Powers (Great Britain, France, Russia, USA) vs Central Powers (Germany, Austria-Hungary, Ottoman Empire)
- Causes: Militarism, Alliances, Nationalism, Imperialism, Assassination
- New warfare: Trench warfare, poison gas, tanks, airplanes
- Aftermath: Treaty of Versailles, League of Nations formation, US return to isolationism