Before we launch world war 3, ask yourself: would you care if Iran, China and Russia were really behind the attacks?
Of course you would.
Well, then you would also want to know whether Bin Laden was really behind 9/11, whether rogue elements within the U.S. allowed the attacks to succeed, or whether it was actually an "inside job".
Think about it. If, like Howard Zinn, you say "I don't care if 9/11 is an inside job", you are really saying you don't care if future attacks are real attacks or false flag attacks intended to justify war against a concocted enemy.
You can eliminate China. They would not kill the golden goose, so to speak. They have to sell all the stuff they produce in our stores.
Iran can be eliminated, since they know that Russia would deal with them as a future threat, if they would have the audacity to start with the U.S.
Russia can be eliminated, since Russia knows that if Germany ever started to play marching music again, the U.S. would once again be on their side.
In effect, the U.S. has no threats that are legitimate countries. That leaves who? I will let you answer that one.