Why did they want to attack the twin towers on 911?

Essentially, he was unhappy with US presence in the Middle East. He wanted American troops out in order to accomplish Al-Qaeda's primary goal of establishing Islamic states in countries in the Middle East and throughout. He hoped that by attacking Americans, he would impose such high costs that our citizens would demand retreat from the area. What he did not count on was the American spirit. Now he is dead.

In lamen's terms, he was crazy and wanted to take over the world. But in order to do that, he would have to get past the US, and that's not going to happen.