Terrorism is just regular war that has more effect on general population & public opinion (usually, but not limited to, done by attacking civil targets or military targets in public view). And everyone uses this tactic - big superpowers or a small group of individuals. The difference is that the small group doesn't even have the option to face a superpower in direct military conflict.

(Like, there is a reason why US bombardment of Japan, including both nuclear bombs, targeted civilian population - just as a definition, it was to inflict terror to get the public opinion & military support to capitulate)

Terroristic acts are a bit more democratic in the sense that they bring small voices to the stage that are otherwise drowned out by domestic propaganda.

(Needles to say but still - all violence of any kind is bad!)