Reading the think-pieces around the two big conflicts can be a bit dispiriting. Having become a commentator, or a publicist, or whatever they're called these days, the writers write pieces saying what the law of nations should be, and then use them for partisan purposes.
The law of nations is precisely what nations have done under necessity, and whatever inferences you can draw from that to the present, with the presumption that things should remain the same, and parties should honor their agreements. But everyone always acts according to necessity. You can't bind a nation in a Lockean or moral-contract sense. Nations feel no guilt, and treaties are frequently "un-signed" these days.
If you're trying to make an argument for an extension of existing law, you're better off trying to predict what nations will agree to, and then inflect that a bit, rather than making an argument about what the law says in itself, so that you can then flog the other side with it if they take the other course. Eventually, that diminishes the power of the idea of international law, which is the most valuable part of international law. It took centuries to build this up, and a lot has been lost in the last five years alone.
Unlike the law of a nation, if the nations don't presently observe a certain precept, that precept no longer exists as a principle of international law.
