The Great War, also known as World War 1, lasted from 1914 to 1918 and involved 65 million soldiers from across Europe and its colonies. Trench warfare led to the deaths of over 8.5 million soldiers while another 21 million were wounded. New weapons like machine guns and poison gas contributed to unprecedented casualties. The war started after the assassination of Archduke Franz Ferdinand of Austria-Hungary led countries to take sides through a system of alliances. The United States initially remained neutral but entered the war in 1917 after German U-boats sank American merchant ships.