In short, 'American imperialism is the root cause of 9/11.' Which happens to be the same explanation of everything since the end of 1991 according to the most dull and, sadly, seemingly most common strain of post-Soviet Marxist thought.

In that Marxism requires massive amounts of violence to push its political stance, and that the system itself views continuous violent oppression as the only way to implement and maintain itself?

Invasion on Afghanistan rendered 9/11 relatively insignificant, except as a trigger - a Franz Ferdinand kind of event.

I suspect Marxist view of that is similar to their view on other cases of US destroying entire regions just to win the next elections.