World War One began on July 28, 1914, exactly one month after the assassination of Archduke Franz Ferdinand, heir to the Austria-Hungarian throne. As Austria-Hungary, determined to respond to the assassination, moved into Serbia (which Russia immediately mobilized to defend), Germany invaded Belgium before moving towards France, causing Great Britain to declare war on Germany and its allies. In less than a week, all of the world’s superpowers, with the exception of the United States, was at war.
The Central Powers were comprised of Germany, Austria-Hungary, the Ottoman Empire, and Bulgaria. The Allied Powers consisted of the rest of the majority of Europe, leade by Great Britian, France, Russia, and, eventually, the United States of America. The U.S. joined the war in 1917, after intercepting the Zimmerman telegram. The telegram was a request from Germany to Mexico asking the Mexican government to declare war on the United States.
The Great War ended on November 11, 1918. Over 9 million soldiers and an estimated 7 million civlians lost their lives in the war. Considered the first “modern” war, it is thought to be one of the bloodiest wars in history.