But uniquely among all countries, they're very likely to be of the same ethnic group, and speak the same language as their rulers. You certainly cannot say that of Brazil, Russia, hell even of the US.

Han Chinese is by far the largest ethnicity on Earth - I've always wondered how that impacts Chinese sentiment and history.

As much as China has a dominant ethnicity, this is only really true in the eastern, core parts of China. In the Northern and Western fringes, plus Tibet, there's entirely unrelated groups of people who, at times, want nothing to do with Beijing.

There are countries with more ethnic cohesion, though they tend to be smaller: Iceland for example. Any larger country either came about by annexing smaller ones, or was sufficiently valuable enough that it was colonized at some point.