September 11, 2001, was a warm and sunny morning with beautiful blue skies. It started out just like any other day—until just before 9:00 A.M. when the first of two hijacked airplanes crashed into the World Trade Center in New York City. At that moment, the innocence and security of a nation vanished as it was attacked by a littleunderstood enemy.

Speculation about who was behind these hijackings—and two others that occurred in Washington, D.C., and Pennsylvania— settled quickly on Osama bin Laden and his supporters in the Arab world. Bin Laden is a wealthy Saudi businessman who started paramilitary camps in Afghanistan in the early 1980s to train Islamic extremists in combat skills and terrorism techniques. His organization was formed to fight the Russians who were then in Afghanistan. After the Red Army pulled out of...