The war was a global conflict. Thirty-two nations were eventually involved. Twenty-eight of these constituted the Allied and Associated Powers, whose principal belligerents were the British Empire, France, Italy, Russia, Serbia, and the United States of America. They were opposed by the Central Powers: Austria-Hungary, Bulgaria, Germany, and the Ottoman Empire. The causes of World War I, which began in central Europe in late July 1914, included intertwined factors, such as the conflicts and hostility of the four decades leading up to the war. Militarism, alliances, imperialism, and nationalism played major roles in the conflict as well. The immediate origins of the war, however, lay in the decisions taken by statesmen and generals during the Crisis of 1914, casus belli for which was the assassination of Archduke Franz Ferdinand of Austria and his wife by Gavrilo Princip, an irredentist Serb.