I belive the most important war was World War I because it redefined the politicsl atmosphere of the world. Corporations really became enthroned, the American socialist movement led by Euegen V. Debs was pretty much completly destroyed by the Sediation Act of 1917 and the Espionage Act of 1918. Before World War I everyone thought the world would always move forward but after World War I that illusion was destroyed. Also it's effect on nations was huge with Woodrow Wilson's Fourteen Points inspiring millions. Finally World War I almost directly led up into World War II.