Is Japan a part of China? Has Japan ever been a part of China? No, Japan is not a part of China and Japan has never been invaded or colonized by China.
Japan and China have a diplomatic history of over 2,000 years. This history began in 57 A.D., when the Nukoku of Japan sent an envoy to pay tribute to Emperor Guangwu of the Later Han Dynasty and was given a gold seal. Among the 2,000 years of Sino-Japanese history, the period after the Opium War in 1840 is considered the modern period. The general view in both countries is that they have been friendly except for the 160-odd years of modern history.
China has always been much larger than Japan. However, China has never attempted to invade Japan.
On the other hand, Japan once invaded China and established the puppet nation of Manchuria. Although this was apparently an invasion by Japan, as Manchuria was not part of Japan on the surface, given its status as a puppet state, it might be correct to say that no territory of China has been a part of Japan.
Taiwan, however, was a part of Japan.
When did Japan independent from China? Japan has never been part of China. China has never invaded or sent military troops to Japan in the entire history.