During World War I, Germany, Austria and the other countries in the Ottoman Empire formed the Central Powers and fought against the Allied Powers, which consisted of Russia, Japan, Great Britain, Italy and France. The war began following the unexpected assassination of Austria's Archduke Ferdinand.
The First World War involved almost all of the world's significant powers. The United States initially was not involved, but joined the Allied Powers in 1917. The war lasted from 1914 to 1918, and primarily consisted of trench warfare. While the Allied Powers were the victors of the war, significant casualties were seen on both sides. It is estimated that over 9 million soldiers died.