Here is a quote from Ye Shi, writing in the late 12th early 13th century when foreign invaders held the north, referring back to a text from the Warring States period.
“One maintains a country with principles, with proper roles, and with the ability to change according to the circumstances. For the Zhong guo (the “Central country”) not to govern the Yi di (tribal peoples) is principle. For the Zhong guo to be the Zhong guo and for the Yi di to be Yi di is the proper role. We are in control of both. Therefore if they come to pillage then we go to war with them; if they come to submit then we receive them; to order them according to their reasons for coming is the ability to change according to the circumstances…The reason the Zhong guo is the Zhong guo is simply because it has these three thing. If we cast aside the tools by which we will necessarily be victorious and merely rely on deceit and force than we will have transformed ourselves into Yi di…However, although the Yi di are unprincipled, they always expect good faith and principle from the Zhong guo. The Zhong guo regards the Yi di as unprincipled and thus responds to them without employing good faith and principle. It does not understand that this is the reason it is the Zhong guo. Basically it cannot abandon something because the Yi di lack it.”