The Chinese claims on the South Pacific Islands seem really similar to me.
Taiwan seems like a wholy different matter. It was united with China for hundreds of years until the Japanese colonialists took over. It united again with China after WWII but split up after a few years because of the Chinese civil war (notice it was an internal war). I think it's just fair that China wants to re-unite with Taiwan, though I definitely don't support a military takeover. Hopefully a solution similar to what was done in Hong Kong can be found. The Tibet region had a similar history and it's definitely unfortunate that China had to use military force to bring it under its own control (arguably completely unnecessarily - China would be just as strong today without it), but it's kind of understandable in the context of the time (China was trying to recover from centuries of being preyed on by other nations).
I am saying this because I can't agree that China is acting imperialistic - it's basically claiming sovereignty over its own historical lands - which were taken away from them by force by foreign colonial powers. But I admit that, if you go back far enough, nearly all land was once taken over by aggressors - the USA being just a more recent example of that.
Anyway, thanks for not being an absolutist and trying to understand the "other" side (I must acknowledge I have no relation to China whatsoever, in fact I am from South America and live in Europe).