Did not this become the Law of Nations by a very gradual drift from "feudalism" wherein the government was vested entirely in individuals - allbeit an interlinked network of individuals? Mutual Recognition was essential to feudalism. It required frequent reinforcement by force of arms.

I have maybe two points. In the period of discussion, many "national" governments were still individuals and inheritance - with all its legalisms including abdication - was a vital consideration.

Additionally today, vastly different nation-states render a "pro-forma" recognition to governments with little consideration of the antecedents -- that is, to reinforce the decision with force of arms if need be and not to shilly-shally about doing so.