I’m already assuming the US will likely come under control of “competent” fascism. I put that into quotes, because no fascist is competent in the long term. You probably shouldn’t assume that you’ll be opposed to a more competent fascist demagogue. If you’re an American that’s fantasizing about a conflict against the “evil within” your own country, you’re already going down the path to fascism yourself.

It’s best to use the same approach as with Franco. Contain and isolate. Most fascist movements die off on their own. Fascists are inherently incompetent, it may take a generation but eventually even Americans will realize it sucks. The biggest concern is obviously the US invading other countries. If there were a civil war in the US, Americans would be shooting all of their ammunition at each other, which makes it less likely they’ll invade other countries. So why should anyone try to be the next USA and intervene in countries they’re not wanted and try to do some nation building bullshit?

If Americans got tired of killing each other, and if a fascist regime didn’t come out on top, and if the US was broken up into smaller countries, only then it would make sense for anyone outside of the US to offer aid. Nobody owes the US anything, and countries should only do what is in their best interests.