The ending of the war in the Pacific, however, provided evidence of how in practice American idealism was tempered by considerations of power. At Yalta in February 1945 Roosevelt behaved in the mould of classic colonial big-power practices. Not only did he make secret concessions to Stalin at China’s expense by agreeing to allow the Soviet Union exclusive rights in Manchuria ( including the use of a naval base) despite the absence of Chinese representation there, but he also undertook to persuade Chiang Kai-shek to accept them. Having made these concessions in order to get the Soviet Union to join in the war against Japan and indeed having agreed at Yalta that the Soviet Union would be one of the four occupying power, the United States in the end defeated Japan largely by its own efforts (including the use of the atom bomb) , and in effect denied the Soviet Union a significant role in the occupation of Japan.