You appear to have no reading comprehension.
English Common Law treated subjects as feudal serfs, tied to the land, once an Englishman always and forever an Englishman. Allegiance to England could not ever be changed as far as English Common Law was concerned
Vattel was the foremost proponent of the constitutional republic in the founding era, you know, the form of governance we ended up with, the one that allows the expatriation that Vattel advocated, that allows people to throw off their allegiance and take up another, to cease being US citizens to become a citizen of another nation if they want?
You’re advocating the thing you think you oppose, and you’re opposing the thing you think you advocate, here.
I am just quoting what Vattel said. I just assume he meant it.