In 1949, the Chinese Communist Party took control of most of China, including Manchuria but not including either Taiwan or Mongolia. Rather than maintain Manchukuo as a Soviet satellite, the Russians looted in, then used it to bolster the position of the People’s Liberation Army. Neither Communist nor Nationalist Chinese forces had the strength the contest this move, but the Soviet invasion of August 1945 quickly annihilated the Kwantung Army.
In 1931 the Japanese Kwantung Army occupied Manchuria and declared it independent of China, installing the last emperor of the Qing dynasty in what became Manchukuo. Japan, however, took advantage of Chinese disorder. Fortunately for China, Russia remained in such disorder that it could not take advantage to its own territorial aggrandizement, and in any case Japanese power held Russia in check.
With the collapse of the Qing Dynasty in 1911, and the ensuing collapse of the Chinese state, China was unable to resist foreign encroachments upon its territory.
