Introduction World War I (1914–1918), also called the Great War , reshaped global politics, society, and economy. Known as the “war to end all wars,” it destroyed old empires, created new nation-states, and laid the foundation for World War II. For UPSC, WWI is crucial under GS1 (World History) , with direct PYQ references. Causes of World War I Militarism – Arms race, German naval buildup. Alliances – Triple Entente vs. Triple Alliance. Imperialism – Competition in Africa & Asia. Nationalism – Balkan crisis, Pan-Slavism. Immediate trigger – Assassination of Archduke Franz Ferdinand (June 1914). Course of the War Western Front: Trench warfare, Battle of Somme, Verdun. Eastern Front: Russia vs. Germany/Austria. Global theatre: Ottoman Empire, colonies of Asia & Africa drawn in. US entry (1917): Shifted balance toward Allies. Russian Revolution (1917): Withdrawal of Russia from war. Armistice (11 November 1918): End of figh...