It's terrorism if you can prove that it's a false-flag operation carried out to smear law-abiding patriots, or if brown people did it. Otherwise, it is something that should not be discussed or remembered at all, because it was clearly a one-time operation by mentally imbalanced lone wolves with no clear or comprehensible motives that has no greater significance for anyone.

AP Style Guide suggests "political violence" to connote historic "deadly incidents motivated by ideology."

This locution juxtaposes "traumatic violence."

Conspicuously absent from exemplars offered is destruction of the WTC.

Diversity is the key to economic and political evolution.