> Legal perspective? The only way you can enforce legality is with force
Dubious. The current legality of the situation is that Taiwan is de jure part of China (PRC), and the ROC is nobody. Nobody is enforcing that with force, it's maintained by the unwillingness of the ROC to provoke the PRC, and the unwillingness of the PRC to risk their credentials and trade over this, or they're hopeful one day the ROC will peacefully join them if relations and trade are good enough.
> Countries gain sovereignty either when ... they have the means to occupy and defend the land they claim is soverign.
Haiti, or much more recently Abkhazia, South Ossetia, Transnistria, North Cyprus, etc. prove this wrong. Even if you have full control of some land and claim to have full sovereignty over it, unless others recognise you, you're in a very bad situation. No international recognition -> no trade or international relations -> perpetually poor.
Dubious. The current legality of the situation is that Taiwan is de jure part of China (PRC), and the ROC is nobody. Nobody is enforcing that with force, it's maintained by the unwillingness of the ROC to provoke the PRC, and the unwillingness of the PRC to risk their credentials and trade over this, or they're hopeful one day the ROC will peacefully join them if relations and trade are good enough.
> Countries gain sovereignty either when ... they have the means to occupy and defend the land they claim is soverign.
Haiti, or much more recently Abkhazia, South Ossetia, Transnistria, North Cyprus, etc. prove this wrong. Even if you have full control of some land and claim to have full sovereignty over it, unless others recognise you, you're in a very bad situation. No international recognition -> no trade or international relations -> perpetually poor.