The Triple Alliance was a military alliance (agreement to fight together) between Germany, Austria-Hungary, and Italy, that lasted from 1880 until the start of World War I in 1914. The three countries promised to help each other if another country attacked them. Some Italian people were not happy about the agreement because Austria-Hungary was an old enemy. In 1914, the Triple Alliance and the Triple Entente (France, Russia and the United Kingdom) started World War I. In 1915, Italy left the alliance and fought against Austria-Hungary and Germany from 1916.