There aren’t any legal restrictions on games from the U.S. as far as I’m aware. At least certainly not with regard to the subject matter you suggested above. Now other countries it might be different. In Modern Warfare 2 terrorists pretty much caused the destruction of D.C. and the obliteration of the White House. But I don’t recall anyone getting offended by that at all, we’re dealing with a fictional story. Though if I’m not mistaken Russia didn’t take too kindly to the level where you play as an undercover agent (U.S.?) and gunned down civilians in an airport with the aforementioned terrorists. Which to be honest I can see their point of view on that, though I don’t think the developers had any nefarious intentions behind it that was simply a major catalyst in the story. I don’t remember if they outright banned the game, or had that level stripped from it.