To commemorate 9-11, the estimable Mideast specialist Prof. Juan Cole has posted a superb quick history and explanation of what al Qaeda wanted to achieve by its despicable act -- and why. In case there are any readers who don't regularly visit Prof. Cole's highly informative web site, let me recommend 'September 11 and Its Aftermath' as an excellent introduction to a Mideast scholar whose skills and insights, sadly, have been in short supply in Washington the past three and a half years.
Here's a small excerpt to inspire you to visit him:
Bin Laden hoped the US would timidly withdraw from the Middle East. But he appears to have been aware that an aggressive US response to 9/11 was entirely possible. In that case, he had a Plan B: al-Qaeda hoped to draw the US into a debilitating guerrilla war in Afghanistan and do to the US military what they had earlier done to the Soviets. Al-Zawahiri's recent message shows that he still has faith in that strategy.
The US cleverly outfoxed al-Qaeda in Afghanistan, using air power and local Afghan allies (the Northern Alliance) to destroy the Taliban without many American boots on the ground.
Ironically, however, the Bush administration then went on to invade Iraq for no good reason, where Americans faced the kind of wearing guerrilla war they had avoided in Afghanistan.