[nl]

I expect his argument is that the former national government of mainland China fled to Taiwan during the revolution.

This is true, but it doesn't make a strong argument for legitimacy. Former governments flee countries frequently, and unless there is a rapidly implemented plan to try to get them back into power they are generally ignored.

Taiwan is better viewed as a breakaway state than having any legitimate stake in the government of mainland China.

[anonymousiam]

One could even argue that the agreement Great Britain had for the 100 year lease of Hong Kong was with the Nationalist (Taiwan) government and not the PRC.

[sudosysgen]

In any case, the treaty is broadly illegitimate as a colonial treaty nowadays.

[samus]

Whether it is colonial or not does not matter for legitimacy. A blanket rejection of treaties on the basis of being colonial and unfair would invalidate all border agreements between former colonial countries.

Of course, the international community can condemn treaties and push for decolonialization, but in most cases this is foiled by the refusal of the colonial power to give up the claim. Examples: Falkland islands, West Sahara, Goa (reconquered by India using military force).

In many cases, it is advantegeous for both parties to seek a peaceful decoloniazation treaty, which becomes a part of international law and formal basis for the future claim on the decolonized territory.

[sudosysgen]

It has a huge impact in practice. The international community will look much more favourably on a country that violates a colonial treaty with its former Metropolis than with any other country.

In practice, colonial era treaties are less legitimate. No one except the parties directly materially affected care.

[nl]

> the agreement Great Britain had for the 100 year lease of Hong Kong was with the Nationalist (Taiwan) government and not the PRC

This appears to be a difficult argument to make in a consistent way. HK was ceded to GB a the Treaty of Nanking[1] which was between the UK and the Qing Dynasty Chinese government. It was later expanded in 1897, again with the Qing Dynasty.

That Dynasty collapsed in the early 20th century. That was followed by the warlord era, and then the nationalist government in the 1930s. That lasted until defeated by the Communist government in 1949.

So there were only around 20 years the Nationalist government governed mainland China, and it was long after the treaty ceding HK.

[1] https://en.wikipedia.org/wiki/Treaty_of_Nanking

[anonymousiam]

So the smart thing for the British government to have done would have been to declare the treaty invalid when the PRC came to power. GB could have claimed Hong Kong in perpetuity and the PRC would not have dared to stand up to GB in that era.