(Hopefully I get this mostly right… I'm by no means an expert, so if I've gotten something wrong, please correct me.)

For the one China thing, see Wikipedia[1]. Essentially, China split into the PRC (mainland China, referred to as just "China") and the ROC (referred to as "Taiwan"). The split was caused by civil war[2]; each side essentially views themselves as "China", the other side being a rebellion. (Though I think Taiwan is split on this, and I believe some of the politics there acknowledges the more defacto reality of two countries.)

Mainland China (the PRC), AFAICT, in propaganda really, really wants you to believe that there is really only one China (them), and that Taiwan is part of that. Hence why they would want the removal of the Taiwan flag emoji. I think to anyone with their eyes open, the de facto state of things is that there exists two countries. But b/c mainland China has a lot of political weight, and only wants everyone else to not recognize Taiwan as a real, independent nation, there is a lot of political dancing-about-the-point to maintain relations with two countries but without outright calling it as it is.

Hong Kong is weird. It used to be a British territory[3]:

> Hong Kong became a colony of the British Empire after Qing China ceded Hong Kong Island at the end of the First Opium War in 1842. The colony expanded to the Kowloon Peninsula in 1860 after the Second Opium War, and was further extended when Britain obtained a 99-year lease of the New Territories in 1898. The territory was transferred to China in 1997.

As you see, that "99-year lease" expired, and it's now part of China again. Hong Kong has operated sort of (but not fully) separately from China, see "One country, two systems"[4]. Then we come to the recent Hong Kong protests[5], in particular:

> The inclusion of mainland China in the amendment is of concern to different sectors of Hong Kong society. Pro-democracy advocates fear the removal of the separation of the region's jurisdiction from mainland Chinese laws administered by the Communist Party, thereby eroding the "one country, two systems" principle in practice since the 1997 handover.

Hence, I think, the rebellions. They (Hong Kong) are worried (I believe rightly) that they'll lose what freedoms they have.

> US has some confusing things too going on, like people from American Samoa are considered US nationals but they aren't US Citizens. They still get US passports, but can't vote, etc. I guess they aren't technically citizens of any country then but aren't completely stateless since still considered a national.

Yep. This never really made sense to me, since supposedly one of the reasons we fought for independence in the first place was things like "taxation without representation". I think you have it mostly correct: they are technically "US nationals", not "citizens". It doesn't make "sense" to me, in that it seems against the principles on which we were founded.

These sort of apply here: "The difference between a terrorist and a freedom fighter is a matter of perspective: it all depends on the observer and the verdict of history." "One man's terrorist is another man's freedom fighter." You have to view this with the context of history, and that there are multiple entities trying to write very different histories if they emerge the victor.

[1]: https://en.wikipedia.org/wiki/One-China_policy

[2]: https://en.wikipedia.org/wiki/Chinese_Civil_War

[3]: https://en.wikipedia.org/wiki/Hong_Kong

[4]: https://en.wikipedia.org/wiki/One_country,_two_systems

[5]: https://en.wikipedia.org/wiki/2019_Hong_Kong_protests