In 1914, a political assassination in Sarajevo set off a chain of events that led to the outbreak of the most costly war ever fought to that date. As more and more young men were sent down into the trenches, influential voices in the United States and Britain began calling for the establishment of a permanent international body to maintain peace in the postwar world. President Woodrow Wilson became a vocal advocate of this concept, and in 1918 he included a sketch of the international body in his 14-point proposal to end the war.

In November 1918, the Central Powers agreed to an armistice to halt the killing in World War I. Two months later, the Allies met with conquered Germany and Austria-Hungary at Versailles to hammer out formal peace terms. President Wilson urged a just and lasting peace, but England and France disagreed, forcing harsh war reparations on their former enemies. The League of Nations was approved, however, and in the summer of 1919 Wilson presented the Treaty of Versailles and the Covenant of the League of Nations to the U.S. Senate for ratification

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