Cao, Liu and Yuan might have thought their kingdoms were

part of one country because they all thought they ought to be the sole ruler of that country.  Tsai Ing-wen?  Does she want to be the ruler of China?  Does she want Taiwan to be part of China?  How about the ordinary folks living in Taiwan?   ("In a Taiwanese Public Opinion Foundation poll conducted in June 2020, 54% of respondents supported de jure independence for Taiwan, 23.4% preferred maintaining the status quo, 12.5% favored unification with China, and 10% did not hold any particular view on the matter." Taiwan independence movement - Wikipedia)