World War I began in Europe in 1914 and lasted until 1918. It involved total war between allied nations on both sides, with all available resources mobilized for victory. The main causes included militarism, as nations increased military spending and preparedness, as well as a system of alliances that drew more countries into the war. Tensions rose due to imperial and nationalist rivalries, as well as a naval arms race between Germany and Britain to control seas and trade.

1. World War I Modern World History

4. Countries Involved in WWI

10. Population Explosion