What event led the Japanese to invade the Chinese province and of Manchuria?

The Japanese invasion of the Chinese province of Manchuria was primarily triggered by the Mukden Incident in September 1931, in which a section of railway was sabotaged near Mukden (Shenyang). Japan used this incident as a pretext to launch a military invasion, claiming it was necessary to protect Japanese interests in the region. The invasion was part of Japan's broader strategy to expand its empire and secure resources amid rising militarism. This aggressive action marked the beginning of a prolonged occupation of Manchuria and heightened tensions in East Asia.