I think the main distinction is who’s doing the attacking. If it’s a state-level attack, then it’s an act of war. If it’s just a random group of dudes, it’s terrorism. It doesn’t become not terrorism just because the target is military in nature.

Which would you consider the Taliban?

Is the Islamic State a state-level organization? How big and well organized does the state need to be?

So all rebels are terrorists, and therefore invalid. Very convenient for dictators.