Soon most of Europe became involved. The Ottoman Empire (now Turkey) joined the war on the side of Germany and Austria-Hungary. It is not clear why they entered or chose to fight on their side, but they had become friendly to Germany. Although Italy was allied with German and Austria-Hungary, they had only agreed to fight if those countries were attacked first. Italy said that because Austria-Hungary had attacked Serbia first, they did not need to fight. They also had started to dislike Austria-Hungary, so in 1915, Italy joined the war on the Allied Powers' side.