Introduction


French and British soldiers in a trench on the Western Front.
World War I was an international conflict primarily involving European nations that was fought between 1914 and 1918. The United States did not enter the conflict until April 1917, but its entry was the decisive event of the war, enabling the Allies (Great Britain, France, Italy, and Russia) to defeat the Central Powers (Germany, Austria-Hungary, Turkey, and Bulgaria). The leadership of President Woodrow Wilson led to both the conclusion of hostilities and the creation of the League of Nations, an international organization dedicated to resolving disputes without war. -- West's Encyclopedia of Law "World War I"