I don't know whether it's the truth, but in my country it's universally accepted opinion among many people that most middle-east terrorists are created and financed by the US. Given the fact that western forces utterly failed to fight ISIS until Russia was involved and then tried to oppose Russia as much as possible (yet Russia still crushed ISIS), it doesn't look very unlikely for me. So one possible way for the world is to have reduced terrorism which might help even the ordinary americans.

Point to ponder: A (small, but potent) bunch of Middle Easterners got very interested in blowing up the USA.

Why did they not blow up Canada, or Mexico, or China? Do you think the US military actions might be a reason?

No idea, but I'm not convinced it would be worse. Maybe we'd try more international consensus and only do UN sanctioned intervention and peace keeping.

Best way to figure it out might be for the US to try it :) (but it seems to go in a different, likely more dangerous way instead: isolationism from the international scene with increased military spending).