World War I
World War I began 28 Jun 1914 with the assassination of Archduke Franz Ferdinand of Austria.
U.S. entered the war on 6 April 1917 when it was discovered that Germany was attempting to get Mexico to join the war on the German side in return for the support in reclaiming the States of Texas, New Mexico and Arizona. Mexico did not enter the war. The U.S. drafted 4 million men and by 1918 was sending 10,000 men a day to the front in France.
The war ended when Germany and the western allies signed a cease fire on 11 November 1918 and later signed the Treaty of Versailles on 28 Jun 1919 to formally end the war.