During this period Manchukuo was used as a base from which to invade China . In the summer of 1939 a border dispute between Manchukuo and the Mongolian People 's Republic resulted in the Battle of Khalkhin Gol . During this battle , a combined Soviet Army and Mongolian force defeated the Japanese Kwantung Army ( '' Kantōgun '' ) supported by limited Manchukuoan forces . The Soviet Union declared war on Japan on 8 August 1945 in accordance with the agreement at the Yalta Conference , and invaded Manchukuo from outer Manchuria and Outer Mongolia . This was called Manchurian Strategic Offensive Operation . The Army of Manchukuo was defeated and the Emperor was captured by Soviet forces . Most of the 1.5 million Japanese who had been left in Manchukuo at the end of World War II were sent back to their homeland in 1946-1948 by U.S. Navy ships in the operation now known as the Japanese repatriation from Huludao
Yalta Conference
Yalta Conference
Japanese colonial empire