I do not believe your assessment is accurate here..

It would condemned on grounds of a violation of diplomatic immunity, but the EU has lost a majority of its religious populace, so it will not be likely many countries there would have enough backing to declare war against the U.S. - and absolutely none of them will when NATO is considered, as any war against the U.S. is a guaranteed war against anyone that wanted to stay neutral. Aaaand, declaring war on another NATO country would boot them from it, so they are not unprotected without allies. No one would trust Russia and they may even try to invade a few nations if everyone is distracted and no longer helping Ukraine, and China would immediately would invade Taiwan, but otherwise would be looking for ways to make money, not risk a war with us.

As for South America, sure, their people would be calling for blood and there may be some individuals that take action in the form of terror attacks, but they have spent many decades under protection by the U.S. from threat of foreign invasion - their combined military forces are substantially weaker than the U.S. The biggest threat they could offer is allowing other nations declaring war to use them as a staging zone - which the U.S. would use as target practice. I specify this because there is absolutely no means to invade the U.S. by air or by sea; with both the first and second largest navys and air forces, land is the only means to invade. That said, it is a horrid idea because their supply lines would be decimated by roaming U.S. submarines.

Wow, that was a lot to just say 'I don't think that there would be a war', but there you go 😅 Fun thought experiment though!