World War I was a global war mostly centered in Europe that began in July 1914 and ended in November 1918. In late June 1914, Archduke Franz Ferdinand of Austria was assassinated by a Serbian nationalist in Sarajevo, Bosnia, and escalating threats and mobilization orders followed, leading by mid-August to war between Germany, Austria-Hungary, and the Ottoman Empire, known as the Central Powers, and Great Britain, France, Russia, Italy, and Japan, known as the Allied Powers. The four years of the Great War brought unprecedented carnage and destruction through grueling trench warfare and the introduction of modern weaponry. Germany’s policy of unchecked submarine aggression against shipping headed to Great Britain brought the United States into the war in 1917. Widespread protest over the sinking of the British ocean liner Lusitania by a U-boat in May 1915 helped turn American public opinion against Germany, and after German submarines sank four U.S. merchant ships early in 1917, the United States declared war on Germany. By the time the war ended in November 1918, more than 9 million soldiers had been killed and 21 million more wounded, while United States casualties totaled 126,000 killed and 234,000 wounded.