The year 2001 began with the inauguration of a U.S. President deliberately aiming to shift the use of the military away from the numerous humanitarian and peacekeeping interventions of the 1990s toward responding to and defeating conventional threats from nation-states. The mood was optimistic, with the new U.S. National Security Strategy, recently put in place by the departing Clinton administration, citing widespread financial prosperity and conveying no sense of an imminent threat to the homeland. But this situation proved fragile: the events of a single day, September 11, 2001, altered the trajectory of the United States and the way it used its military over the next decade. A nation focused on countering conventional threats was now confronted by an enemy that attacked the homeland with low-tech means in asymmetric and unexpected ways—individuals armed with box-cutters using hijacked civilian aircraft