Japanese invasion of Manchuria
The Empire of Japan's Kwantung Army invaded the Manchuria region of China on 18 September 1931, immediately following the Mukden incident, a false flag event staged by Japanese military personnel as a pretext to invade. At the war's end in February 1932, the Japanese established the puppet state of Manchukuo.
Source: Wikipedia — Japanese invasion of Manchuria (CC BY-SA 4.0)