Lets start with the least menacing and work up.
At the bottom we have the big brother terrorist. You know the kid that can't keep from torturing little sis. Be it spiders, worms, squished frogs, ratings based on the level of scream reaction, if she really does tell mom, and if dad gets involved, being the most points.
Then the little brat grows up and becomes the school terrorist. YA know, head in toilet, thumbtack on the seat, and the ever popular, "locker escape".
Then, comes college. Oh, the things we learn in college. How to properly assemble a Molotov cocktail, pipe bomb 101, chemistry comes in handy, but those are usually for weekend entertainment. The more "serious" types protest, and get beat up.
Moving into the more dangerous terrorist types, we have "lone nutcase", disgruntled employee, pissed off driver, and haters of the IRS. These types usually don't have much of a plan, and after one outburst they're done.
Then we have a fairly new group to the terrorist party, but effective nonetheless. Militarized police. Testosterone run amok. This is a formally trained group, with funding from the government, and supplies, and training, from the military. The old "to protect and to serve" has been replaced with "GET ON THE GROUND, DO IT NOW." and "DO YOU WANT TO GET TASERED AGAIN"? And for those, "oops" moments they have the "I thought he had a gun", which excuses all murders committed while keeping the community "safe".
Next we have "international terrorism". Not too sure what they do, but they get blamed for a lot of stuff.
And the grand daddy of all terrorist groups..........The United States government. The pain death and suffering this group has unleashed on the world is incomprehensible. The pain death and suffering it has unleashed on it's own people, is unforgivable. One small group attacks this sick cabal, and entire countries are obliterated. Aspirin kills more people every year, than that small group of evil genius box cutter banditos did on 911. And, yes, the US bombed an innocent aspirin factory.