The Empire of Japan took advantage of instability in China and a weak League of Nations and established a "puppet" state in North-East China in the early 1930s. Japan could easily send troops through Korea (which had been part of the Empire of Japan since 1910) into North-East China. It gave Japan access to the natural resources of the area as well as a large land base from which to stage their invasion of China. The first stamps were issued in 1932 and the last ones in 1944. Some of the issues were overprinted and used in other parts of China, particularly in the north east provinces during the turbulent time between the defeat of Japan and the Communist takeover of China (1945 – 1949).
Stamps of Manchukuo are quite collectable, even for the average collector. They are reasonably distinctive. There are a small and limited number of issues. No issues are so rare as to be extremely expensive. An essentially complete collection can probably be put together for less than $500. And there are enough variations in stamp design, and enough errors, to keep interest.
Stamps East is the online Canadian source for stamps and other philatelic items from the People's Republic of China (China, PRC), the Republic of China (Taiwan, ROC), and other stamp issuing jurisdictions in Asia particularly East Asia.