In 1939, the Japanese attacked west from Manchuria into the Mongolian People's Republic after the 1938 Battle of Lake Khasan. They were decisively beaten by Soviet units, under General Georgy Zhukov. After the battle, the Soviet Union and Japan were at peace until 1945. Japan looked south to expand its empire, which led to conflict with the United States over the Philippines and the control of shipping lanes to the Dutch East Indies. The Soviet Union focused on its western border but left 1 million to 1.5 million troops to guard its border with Japan.