The battles of World War I were fought on an unprecedented scale. Both sides made use of industrial technology to inflict horrendous numbers of casualties on the other and armies composed of millions of men confronted each other in cataclysmic encounters, the like of which had never been seen before. On one side were the Central Powers of Germany and the Austro-Hungarian Empire, who were joined by the Turkish Ottoman Empire and by Bulgaria, while the other was made up of the Entente Powers, the Allies of France, Russia and Britain, together with the countries of the British Empire and Commonwealth, principally Canada, India, Australia, New Zealand and South Africa. Over the course of the war, other countries also joined the Allies, including Italy, Romania and, in April 1917, America, whose vast resources of manpower and huge industrial capacity dramatically altered the balance of power on the battlefield.