I don't think this is terrorism, that's not what the word means. It's a clear and open act of war, so in many ways much worse, but somehow terrorism is a scarier word.
English is not my first language. If you got a better word other than American terrorists and American terrorism, then suggest me one.
It is, because it might impact normal citizens. Nobody has ever invaded US so coensequences of real war are unknown to most.
That's not technically true, seeing as how Washington DC was captured and burned in 1814. But it's at least true for modern times.