You guys, sorry to say but it did happen. And if you're thinking there is something fishy with the entire thing, there is.
I would like to turn your attention to a small part of history after the end of the cold war
http://en.wikipedia.org/wiki/Soviet_war_in_AfghanistanIt starts to get interesting at "Insurrection" and "Foreign involvement and aid to the mujahideen"
Basically in the years before 1979, Afghanistan was building up some tension due to the feuding political bodies at the time. After a few mishaps and "accidents", it broke up into an all out revolution. The Soviet Union, much earlier on at 1919, had formed several agreements and Afghanistan effectively became the Soviet's pet project. Russia had become in charge of the military training of the afghan military and began providing other types of aids as well.
In 1979, the afghan governing body requested military action from the Soviet to help quell the turbulence. So the soviet dispatched regimes and began siezing control of the country.
Now where it gets interesting is when the US gets involved. At the time, the US were trying to seize control of the Persian Gulf, where all the fancy oil stuff was at the time. Anyways, the US decided "Oh ho them nasty soviets coming too close to our oil, let's help the afghan resistance!" and they armed and trained the resistance to combat the Russian forces. Russia withdrew, and the US immediately stopped all support for the resistance forces and simply left the scene without really giving a care to the fate of the country. That resistance dissolved into several groups who began feuding after they had seized control of the country. One of these groups became the Taliban, and they took control of the country up until 2001 when the US got pissed because they used those training sessions the US provided to them a few years back to infiltrate the US and the rest is history.
So the US indirectly caused the whole 9/11 thing by getting loving involved in a war they were simply not supposed to stick their nose in in the first place. But really, don't take my word for it, go read up on some articles. Avoid any media-related stuff though, the media is idiotic and 99% of their facts are baseless and not the entire story if ever right.
