April: Italy joins the war

Italy had been allied with the German and Austro-Hungarian Empires since 1882 as part of the Triple Alliance. When the war broke out, they did not join on the side of the Triple Alliance. Italy argued that the Triple Alliance was defensive in nature, and that Austria-Hungary now was an aggressor. Italy remained neutral the first year of the war, but in April 1915 they joined on the side of the Triple Entente, breaking their bonds with the Triple Alliance. Italy declared war on Austria-Hungary in May 1915, and fifteen months later they declared war on Germany.