As a nation, we can breath a sigh of relief and know that justice has finally been done. But if we want to ensure that this sort of thing never happens again, we should look past the foolish notion that "the terrorists hate us because of our freedom."
It was no accident that the World Trade Center was one of the targets, along with the Pentagon and the White House. What is it about our international trade policies and foreign relations that would foment so much hatred? There is no justification for taking innocent lives. None. But not to ask why is simply irresponsible.
If you are willing to ask the question, here are some books that might help with the answer:
Blum, W. (1995). Killing Hope: U. S. Military and CIA Interventions
Since World War II. New York: Common Courage Press.
Kwitny, J. (1986). Endless Enemies. New York, New York: Penguin.
Perkins, J. (2005). Confessions of an Economic Hitman. New York: Plume.