The PRC claim to Taiwan is about as weak as can be. They have after all _never_ ruled the island. The mainland and Taiwan have only been unified (if you can call the 45-49 “unified”) for four years in the last 125 years. Moscow ruled Ukraine up until a generation ago (not that I think that gives Russia any claim to Ukraine).
The PRC’s claim to Taiwan is ludicrous.
I think you got it backwards: Taiwan's claim on China is more valid - after all, they are the original China unspoiled by the demon of communism.
I don't say that to support the CCP - the only legitimate government is one chosen by the Chinese people - but saying "Taiwan and the North were the original governments" is plainly false. The Confuscian emporers, going back 2,000+ years and lasting until ~1911 (with many interruptions), would have by far the best claim on 'original government'.
I absolutely support the freedom of the people in Taiwan - and of those in all of China, though only the ones in Taiwan have it - but the parent doesn't make sense to me:
What is the "original China"? Imperial, Confucian China, which (including many interruptions) goes back over 2,000 years, and ended in ~1911? The predecessors to imperial China? Neither has anything to do with the Nationalists (who fled to Taiwan when they lost the civil war to the Communists).
Which region would that be?
Their military spending is less than France and Germany combined.
I expect so. But China is a great power, and Russia is only a regional power. It's much easier and cheaper to isolate Russia.
China's claim on Taiwan is 1000x more valid than the Russian claim on Ukraine, and the world would react differently. I say this as someone who likes the RoC, and thinks they have a right to self-determination.
Ultimately, though, China is trying to win the economic and political game. You need a large military to play that game as a great power, but you don't have to actually invade people to exercise military power. And wars are terribly costly when you're trying to modernize infrastructure. Decoupling China from the US would be terribly costly to both sides, while trade is profitable. So they use that to buy a sphere of influence, largely in Africa and South America. Putin is the idiot who still thinks he can invade his way to a sphere of influence, which hasn't really worked out for anyone after the Spanish-American war.