I have seen absolutely no credible evidence to suggest that the 11 September 2001 attacks were a result of any kind of conspiracy by the U.S. governments or anyone outside of the Al-Qaeda network. It was indeed a terrorist attack planned and carried about exclusively by Al-Qaeda.

There were major intelligence failures by the Bush administration that they have tried to cover up. There were also disingenuous efforts to try to blame the attacks on Saddam Hussein’s regime in Iraq and other efforts to take advantage of the tragedy to advance Washington’s imperialist agenda in the Middle East. The insistence on portraying the efforts to counter the threat from Al-Qaeda as a U.S.-led “war” rather than an international anti-crime effort allowed the U.S. government to dramatically increase military spending at the expense of needed domestic programs and dramatically extend the U.S. military presence in the greater Middle East.
 
Al-Qaeda was largely driven out of Afghanistan by the end of 2001, but U.S. troops remain in that country to this day.  The administration took advantage of the fear from the 2001 attacks to build up support for the 2003 invasion of Iraq, despite the fact that Iraq had nothing to do with it, that Saddam was a strong opponent of Al-Qaeda, and the U.S. invasion and occupation not only took attention away from fighting Al-Qaeda but created conditions for the dramatic growth of Salafist extremism in Iraq and elsewhere. Furthermore, the United States maintains close ties to Saudi Arabia despite the regime’s support for Salafist extremists, again underscoring the United States’ lack of seriousness is challenging such dangerous tendencies in the region.