> China was an Empire because they tried(and succeeded) taking over neighbours by force, including Mongols and Japanese.

Uhm... You clearly have no idea about China.

First, it was _itself_ conquered by Mongols ( https://en.wikipedia.org/wiki/Mongol_conquest_of_China ). Who were then simply assimilated.

Second, China has never conquered Japan.

Overall, China has been remarkably non-aggressive.