The US was attacked just as the US has attacked many other nations over the years. How and why the towers collapsed is not so important although it seems probable that the collapse was caused by the impact of the planes and the subsequent fires weakening the structure and causing a classic vertical demolition to result. For the real conspiracy look at why the Teleban did this- because the US demanded the Teleban provide secure route for Unocals proposed pipeline taking oil fro Khazakstan- the Teleban response was that Unocal must negotiate with each provincial leader if they want to build and secure their pipeline was not met with acceptance from Washington. The US imperialist was shown it cannot demand what it wants from the Teleban who again rule this resource rich but hugely impoverished strategic geography.