It was dependent on having modern technology, like a truck and cheap fertilizer; it's a lot harder to kill 168 people (and wound almost 700) with an oxcart and a crossbow. Even with a carriage and black powder you need a _lot_ of people to be in on the plot. (Black powder was not cheap, not deniable, and not easily transported or concealed.)

What about poison? or fires? I'm sure there's other means I can't think of right now

Modern tech has made it a bit easier, but it was still fairly easy throughout most of history.

It was not easy to get enough poison to kill hundreds. You get some hemlock, dump it in a well, and it dilutes enough that a dozen people get stomach aches and one elderly person dies. It's feasible to pull this off on a larger scale, but you'd need a lot of poison, and therefore a lot of resources.

Fires? I'm not sure it was that easy to set an out of control fire that would consume enough of a town to kill hundreds. Does everyone just fail to notice as you splash pitch on buildings all day leading up to the final act of starting the fire at night?

Pitch, or indeed much premeditation at all, wouldn't be necessary in a village with five foot alleyways and dried grass roofs. Additionally, tar was a common caulking material. Oh, and running water/chemical foam wasn't usually a thing. And, you know, no trained quick response teams, or well maintained roads and swift transit systems to escape on, or any way to tell the difference between the smoke that always hung around the fireplace and the smoke from the roof being on fire... I could go on.

Face it people -- terrorism is a problem of technology.

Exactly. Primarily the technologies of mass media and democracy.

Of terrorism, the newscasters on TV who sensationalize the act and the politicians who fan the flames for their own benefit are just as guilty as the person who blew themselves up.

(Though obviously, only the latter is guilty of murder)