And then came Iraq's invasion of Kuwait and an American and U.N. military operation known as "Desert Storm." Critics claimed the real motive for fighting was oil; President George Bush insisted it was a matter of principle, and that Iraq's leader, Saddam Hussein, had to be stopped.

"The evil against the good was so clear, it made it very easy for me. It was an easy call for me on principle—not on execution," he said. "I think Desert Storm lifted the morale of our country and healed some of the wounds of Vietnam. I'm sure of it."

But in fact, a much broader, invisible war was escalating as fundamentalist extremism continued to spread throughout much of the Muslim world. And over the next decade, during the presidency of William Jefferson Clinton, membership was rapidly expanding in a secret terrorist network known as al-Qaeda.