Yes, what you wrote is probably quite true:"Like you said terrorism is a phenomena that has really elevated since the 70's and 80's and also seems to be centered on the extremely difficult issues of Israel and Palestine. The USSR never played anywhere near as big a role as the US did in the Israel/Palestine problems." And there are probably other factors as well which might skew the scales. The U.S.S.R. was hated by many within the country and by many in the Soviet Bloc countries in Europe, and these people may not have been as likely to commit terrorism (especially if they had relatives who would suffer for their actions). As Andy Fox points out, we may not have heard of every incident. However I think we definitely would have heard of incidents which could have occurred outside the U.S.S.R., such as attacks on embassies.