If you're speaking of China as in the PRC, the history goes back less than a century and its territory has only expanded. If you're speaking of the region, then in reality Europe has a history of being even more divided. Nobody wants to see their homeland being taken away or families separated.
>"They just want to take back what used to belong."
How is this different from various historical German ideologies that have centered around "taking back" Greater Germany including the former holdings of the Holy Roman Empire or Prussia? Consider that Otto von Bismarck was still alive when Taiwan was part of Japan.
The desire to fully restore the borders of the Qing is completely understandable and even laudable from the Chinese perspective. The problem is that it's nearly impossible to have a peaceful world if every national or ethnic group feels justified in using the historical borders its ancestors once held as a bar for what they need to "take back", by force if necessary.
On the specific issue of HK, it's been part of China for a very long time and only taken away recently. Of course we are not talking about taking back European territories that used to belong to some dynasties briefly. Just those stable ones since Ming and Qing dynasty. As another comment pointed out, although China has been divided many times, the geographic boundaries did not change much, unlike Europe.
Taiwan is more debatable because it was separated from China geographically, culturally and economically for very long periods of time.
It is actually much complicated than those maps showing only one governing body. Actually those maps show precisely the periods of unity (Han, Tang, Yuan, Ming, Qing) where only one major power governs, as well as the periods of divisions where foreign ethnicity capture a sizable portion of China.
In latter case, the map fails to capture the lost boundary, like in this case: https://en.wikipedia.org/wiki/Jin_dynasty_(1115%E2%80%931234... where Jin dynasty is in control of majority of the territory and the map only shows the defeated Northern and Southern Sung dynasty. Actually the website that you quoted from also has the information:
> brutal invaders drove the Chinese from their northern territory, forcing them to migrate south and establish a new capital city.
>"They just want to take back what used to belong."
How is this different from various historical German ideologies that have centered around "taking back" Greater Germany including the former holdings of the Holy Roman Empire or Prussia? Consider that Otto von Bismarck was still alive when Taiwan was part of Japan.
The desire to fully restore the borders of the Qing is completely understandable and even laudable from the Chinese perspective. The problem is that it's nearly impossible to have a peaceful world if every national or ethnic group feels justified in using the historical borders its ancestors once held as a bar for what they need to "take back", by force if necessary.