It allowed the US forces to advance their troops onto Afghanistan and united the whole of America behind the cause. This benefitted the US both financially and politically.
Iran was planning to trade their oil in currency other than USD. Esssentially lowering the value of the Dollar.Iraq had already begun trading in currency other than USD. The Attacks of 9/11 put the U.S. in the two main positions to make a "show of force" to Iran as well as seize Iraq oil.
The security of WTC and an airport involved were enforced by the same family that funded the terrorists. Additional suspicion also arises when Bertha Champagne dies in the Bush's driveway, crushed by her own car, which then drove past the checkpoint and into the woods.