In 1945 during a heavy fog a B-52 bomber accidently hit the Empire State building, sustaining minor damage but was repaired and is still standing today, because of this incident modern skyscrapers are specifically designed to withstand an impact from a jumbo jet.
In 1993 terrorists ignited a truck bomb beneath the twin towers after that incident the towers were regularly inspected with bomb sniffing dogs, these inspections stopped just months before 9/11 Marvin Bush was in charge of security at the World Trade Center.
In 1998 the Project for the new American Century or PNAC stated their goal of invading Iraq and overthrowing Saddam Hussein, but said they would need a "Pearl Harbor" to sell this idea to public, key PNAC members became part of the Bush Administration.
The towers did not collapse from the initial impact, many people were safely evacuated and the towers collapsed some time later. The government claims burning jet fuel softened the steel support beams causing the collapse. Jet fuel burns at a maximum temperature of 1500 degrees, the steel would have to reach 2000 degrees before it even began to soften, steel melts at 3000 degrees.
If the steel beams did get hot enough to soften, the towers should have tipped toward the point of impact, but instead the towers collapsed straight down like when explosives are used for a controlled demolision.