text: It's a good thing you don't want just a one or two line response; it's never quite that easy.\n\nFirst, it comes from a sense on the part of al-Qaeda that the U.S. is the "Great Satan."  What initially set these guys off was when the U.S. deployed to Saudi Arabia to fight Iraq in 1991.  The mudjaheddin believed they should be the ones fighting the Iraqis -forgetting that most of their weapons & support came from the U.S. anyway.  Being passed over in favor of the U.S. was a big irritant.\n\nSo, because of what amounts to a huge inferiority complex, they felt (and still feel) the need to hurt the U.S.  After the 1993 World Trade Center bombings, the disaster in Mogadishu, the 1998 embassy attacks in Africa, and the USS Cole attack, they figured the U.S. didn't have the guts to use force against them, beyond firing a couple of cruise missiles which may or may not have done anything serious besides blow up an aspirin factory in Sudan.\n\nThe Clinton administration didn't do anything to disabuse them of this notion; to their credit, mustering the kind of support needed would have been difficult in general, and impossible under his key supporters.  After several years of planning, 19 terrorists hijacked four airliners, and we all know the rest.\n\nPart of this was hoping that the U.S. would invade Afghanistan and then al-Qaeda could somehow cause the country's collapse.  Why did they think this?  Because, less than two years after the end of the Soviet occupation, the Soviet Union collapsed.  Any serious student of international relations knows, of course, that such thinking is, to say the least, deeply flawed, but that's what they thought.  Al-Qaeda also believed that we would deploy tanks & infantry and do what the Soviets did, assuming, of course, we would even have the will to fight, which he didn't believe we had.  So, what did happen came as a major surprise.\n\nHonestly, if anyone thinks that someone else caused 9/11, they're crazy.  Al-Qaeda did it after failing to blow it up in 1993.