Actually, we can declare war on another country, Afganistan. They are directly guilty of knowing and allowing people in their country to conduct acts of war against us.
I don't like the use of the word Terroism, because thats a tactic used by people, not an actual entity you attack.
At any rate this has more in common with going after Mobsters than it does going after Nazi Germany and Japan. The problem is the mobsters are in other countries. Their governments have to be held acountable for keeping their citizens from commiting crimes. Thats what the governments are for.