The twin towers had always been targets of terrorist attacks because it was seen to be like a symbolic strike to the heart - Take down the big and famous land mark and people will notice. They had been bombed before with far less damage. On 9/11 the terrorists worked out a way to really do damage. The design of the Twin Towers was an exoskeleton type - So the main strutural support holding the floors up was the vertical steel exterior beams rather than depending on the interior pilons only, this technique was employed at the time of building because it would make construction of the towers a quicker process. When the planes crashed into the building, they sliced through the vertical beams on the exterior, weakening the main structural integrity and then gravity did the rest. Whilst it is true that the US is oil hungry, and the Afganistan/Iraq are the result of this agenda, it also has to be remembered that there are in fact bad people in the world, who would not blink in harming someone they don't like. Monday Morning in Melbourne CBD anyone?