Foreign terrorism is rare, because it's hard to carry such a thing out in an alien land, and very few people are interested in foreign aggression that is clearl

Foreign terrorism is rare, because it's hard to carry such a thing out in an alien land, and very few people are interested in foreign aggression that is clearly (a) targeted toward civilians, (b) illegal by any national standard, and (c) not part of any coherent political agenda, but merely an artifact of unfocused anger. Domestic terrorism (where the foot soldiers believe they're an occupied people and often see themselves as a legitimate military) depends on where you are and the political climate. That can become a recurring threat, as in Israel. For all the flaws of the U.S., we have one of the most ethnically inclusive societies in the world. We're far from perfect, but we don't have the specific class of injustices, at a high enough level, to produce the simmering grudges that cause such a thing to happen. Most of our terrorists are lone nutcases. Relatedly, Americans and Northern Europeans tend to be culturally individualistic, so the people who would be domestic terrorists tend toward spree violence with either no political mission, or one that is not charismatic enough to post a threat of recurrence. For example, as horrible as Breivik's attack in Oslo was, it didn't motivate a wave of similar attacks. He had a political agenda, but not a coherent one that many people would follow. TL;DR: Terrorism has many forms, and some pose high rates of recurrence, but foreign terrorism tends to occur in one-off attacks and the U.S. does not presently have the conditions (or, at least, does not seem to have them) that would cause recurring domestic terrorism.