If anything, it was the Slavs in that region that expanded eastward and resettled conquered territories e.g. Tatars(Crimea) to the eastern parts.
Taiwan was inhabited by Austronesians, some of which were butchered by the dutch when they first drove them out, then by Portuguese, later by the Japanese (for a while a lot of Taiwanese considered themselves Japanese, while others on that Island fought of the invaders in the east) and sometime in between all that Hakka and other Han Chinese settled the island.
After loosing the civil war as you know Chiang Kai-shek settled there while running a brutal dictatorship where the first thing he did was take all the local currency and reissue his own. I think the biggest giveaway on how problematic Taiwans history with China is, is that some of the biggest treasures that Mao tried to destroy are in the national history museum in Taipei.
I agree with you that Taiwan never accepted changing it's own constitution(i.e. passports are still issued as RoC, not as Taiwan), but you absolutely cannot compare Ukraine to Taiwan. Neither in geography nor in history.
