Japanese puppet state in Manchuria (1932–45). Using the Mukden Incident as a pretext, the Japanese seized the city of Mukden in September 1931 and within five months had extended their power over all Manchuria. Japanese expansion to the west was halted by the Soviet army in 1939, but the Japanese remained in control of Manchukuo until the Chinese communists (with support from the Soviet Union, who removed large quantities of industrial equipment) took over at the end of World War II.