Essay from Al-Qa'ida spokesman Suleiman Abu Gheith explaining why they're fighting the U.S.
We have not reached parity with them. We have the right to kill 4 million Americans – 2 million of them children – and to exile twice as many and wound and cripple hundreds of thousands. Furthermore, it is our right to fight them with chemical and biological weapons, so as to afflict them with the fatal maladies that have afflicted the Muslims because of the [Americans'] chemical and biological weapons.