At the milder end of the spectrum are the theorists who believe that the US government had prior warning of the attacks but did not do enough to stop them. Others believe that the Bush administration deliberately turned a blind eye to those warnings because it wanted a pretext to launch wars in the Middle East to usher in another century of American hegemony. A large group of people - collectively called the 9/11 Truth Movement - cite evidence that an airliner did not hit the Pentagon and that the World Trade Centre could not have been brought down by airliner impacts and burning aviation fuel alone. This final group points to video evidence which they claim shows puffs of smoke - so-called demoliton squibs - emerging from the Twin Towers at levels far below the aircraft impact zones and prior to the collapses. They also believe that, on the day itself, the US air force was deliberately stood down or sent on exercises to prevent intervention that could have saved the lives of nearly 3,000 people.