China is not an expansionist imperial power as your comment seems to imply, quite the opposite, it always talks about how they have no intention to expand beyond its borders... but of course, it sees Taiwan as an internal affair (and most other countries in the world acknowledge it and accept its one-China policy). Taiwan was very much a part of China before the Japanese invaded it in 1895 [1] (though it had also been temporarily colonized by European powers before then), and again once the Japanese lost the war in 1945. Taiwan was then controlled by the Republic of China (ROC) "Party". When the civil war ended in 1949, the ROC lost to the Community party in mainland China and millions of its members fled to Taiwan[2] and hoped to later unify China with itself, but that obviously never happened. They continued to claim to be the legitimate government of all of China (and even parts of neighbouring countries), and apparently some of them still do!
From the Wikipedia article:
"The ROC was a founding member of the United Nations, and held the seat of China on the Security Council and other UN bodies until 1971, when it was expelled by Resolution 2758 and replaced with the PRC. Since 1993, the ROC has petitioned the UN for entry, but its applications have not made it past committee stage.[281][282] Due to the One China policy, most UN member states, including the United States, do not wish to discuss the issue of the ROC's political status for fear of souring diplomatic ties with the PRC."
I believe both sides actually want an eventual unification, Taiwan just doesn't want to lose all its autonomy and have a change of political system (it's a democracy, unlike mainland China).
If China can convince Taiwan to democratically rejoin the PRC then that’s fine. If they do it using military force then the issue isn’t really that complicated.
From the Wikipedia article:
"The ROC was a founding member of the United Nations, and held the seat of China on the Security Council and other UN bodies until 1971, when it was expelled by Resolution 2758 and replaced with the PRC. Since 1993, the ROC has petitioned the UN for entry, but its applications have not made it past committee stage.[281][282] Due to the One China policy, most UN member states, including the United States, do not wish to discuss the issue of the ROC's political status for fear of souring diplomatic ties with the PRC."
I believe both sides actually want an eventual unification, Taiwan just doesn't want to lose all its autonomy and have a change of political system (it's a democracy, unlike mainland China).
This issue is really complicated.
[1] https://en.wikipedia.org/wiki/Taiwan#Japanese_rule_(1895%E2%...
[2] https://en.wikipedia.org/wiki/Retreat_of_the_government_of_R...