Where the Blame Really Lies

The two historical events that contributed to the 9/11 are the Soviet Invasion of Afghanistan, and Saddam’s invasion of Kuwait.
It was the Soviet Invasion of Afghanistan which allowed the global jihad movement to get off the ground. (And allowed Bin Loudin to gain experience) After the Soviets withdrew from Afghanistan, the jihadists became more embodied. Having defeated the Soviets, they then set there sights on the US.
After the invasion of Kuwait by Saddam Hussein, the US sent troops to Saudi Arabia, where they stayed for over a decade. The presence of "infidels" near the most sacred sites of Islam enraged many of the jihadists and may have very well made terrorism against the US more likely.
Without these two events, its doubtful that the attacks of 9/11 would ever had happened.