Nothing about it was illegal. The Japanese surrendered to the allies and did sign the peace treaty giving up the islan, by treaty, to US occupational control. At the time, the ROC was not on the island and the US had them act on their behalf.Then US got a bigger problem on its hands,
if it is still occupying the territory of another country, I would say pretty illegally....
because pretty much all international bodies and countries, including United States, recognizes Taiwan as part of China, even back when US recognized ROC as the official government of china.
and the PRC in 50s up to late 70s were pretty much right in pointing out that US is occupying Taiwan and should be thrown out as an invader.
better settle this before People's Liberation Army really knocks on the door.
After the ROC lost the war on the mainland the issue was in question and the US left it that way.
Nothing illegal there...just not settled legally on paper, though the ROC is governing as though it were...but doing so acting on behlaf of the US on paper who is okay with it...which means it would all also be legal.
Sort of like the Korean conflict, after all of these years is still not "officially" over. Just an armistices/cease fire but no formal treaty.
So it apparently is with Taiwan. The US it seems, is just letting it go until the two sides come together, and in the mean time, the ROC governs with US approval the whole time.
The US has indicated that there is one government of China...but on paper, legally according to the treaties...that does not yet include the island. Realize, this is all legaleze stuff...has nothing to do with the reality of the situation on the ground. It is clear that the US wants both sides to work this out peacefully.
No need to threaten military action over that...to do so would be a worse action by the PRC, and give up all the good will they are developing by waiting as it is.
I believe it can, and hope and pray it will, work out peacefully. It's just an interesting bit of research on the actual treaties and the history that have legally been involved with the island since the 1895 treaty.