9/11 isn't even close to the beginning of the end of the Westphalian order. The increasing domination of multinational corporations, labor organizations, political movements, terrorist organizations, etc., was widely observed and pointed to as evidence of the progressive decline of the nation-state order for many decades prior to 9/11.
While I don't disagree, it's still true that much (though not all) of trans-national activity still takes place within an overall Westphalian state framework. (And one of the big exceptions--the Middle East--is essentially a result of the collapse of the Ottoman Empire post-WWI.
