Earlier quoted context omitted.
>We live in a world where the government can drop a nuke on Japan, vaporizing tens of thousands of civilians (including some American POWs), and that's 100% legal. hahaha, ok maybe you are just insane. How is that legal, are you invoking the Bush doctrine[0] of pre-emptive strikes, although to call that legal is a stretch. Are you suggesting that during a declaration of war it becomes legal? Currently under internati…
The Constitution is a domestic instrument. It does not limit what the United States can do abroad, and the founders were clear that it wasn't meant to do any such thing. Indeed, the concern during the drafting was not about how to limit the government's powers abroad, but how to ensure that it could still act as a sovereign entity abroad despite being limited domestically.
The Constitution is the basis of all US government authority, it is not merely a "domestic instrument".
> It does not limit what the United States can do abroad,
Several provisions of the Constitution directly and explicitly concern what the United States can do abroad, and which institutions of the United States government are entitled to do those things, so that seems an implausible interpretation.
> and the founders were clear that it wasn't meant to do any such thing.
The founders were quite of different minds on many points, and you can often find founders on multiple sides of any issue (including matters of Constitutional interpretation.) Where's the evidence that the founders, collectively, were "clear" on this point?
> As for "international law"--there is no such thing.
The Constitutions grant of power to Congress to "To define and punish [...] offenses against the law of nations;" certainly seems to suggest that they thought that the "law of nations" was not a phrase that referred to something nonexistent.
> The U.N. is not a sovereign entity
No, its a product of treaty, ratified by the US Senate under the provisions laid out for such in the Constitution.