World War I was started mainly due to Web of Alliances. One country attacked another country which attacked that country, then another country and so on. It was fought between the Entente Powers (United States, France, British Empire, and the Russians) and the Central Powers (Germany, Austria-Hungary, and the Ottoman Empire). World War I also saw the beginnings of trench warfare which mostly was in the Western front since combat in the Eastern Front was more fluid. The war ended in 1918 with the Treaty of Versailles formally ending it in 1919. By the end of the war the total number of military and civilian casualties was around 37 million.