9/11 conspiracy theories allege that the September 11 attacks in 2001 were either intentionally allowed to happen or were a false flag operation orchestrated by an organization with elements inside the United States government. A poll taken in 2006 by Scripps Howard and Ohio University showed that, "More than a third of the American public suspects that federal officials assisted in the 9/11 terrorist attacks or took no action to stop them so the United States could go to war in the Middle East."
The most prominent theory is that the collapse of the World Trade Center and 7 World Trade Center were the result of a controlled demolition rather than structural weakening due to fire. Another prominent belief is that the Pentagon was hit by a missile launched by elements from inside the U.S. government or that a commercial airliner was allowed to do so via an effective standdown of the American military. Motives cited by conspiracy theorists include justifying the invasion of Afghanistan and Iraq, geostratigic interests in the Mideast including pipeline plans launched in the early 1990s by Unocal and other oil companies.
Published reports and articles by the U.S. National Institute of Standards and Technology, Popular Mechanics and mainstream media have rejected the 9/11 conspiracy theories. The civil engineering establishment generally accepts that the impacts of jet aircraft at high speeds in combination with subsequent fires, rather than controlled demolition, led to the collapse of the Twin Towers.] NIST states that they did not perform any test for the residue of explosive compounds of any kind in the debris.