Since the Sept. 11, 2001, attacks, the United States has pursued al Qaeda across the globe, and the international community largely has united in the fight against terrorism. However, al Qaeda by nature is ill-defined and elusive, placing small "cells" in specific areas and avoiding an easily discernible command structure. The public perception in the United States largely has been that the four teams that carried out the Sept. 11 attacks were the only al Qaeda operatives in the country at the time, and that they carried out the coordinated hijackings with minimal supervision from overseas. From al Qaeda's perspective, however, this would make little sense. Acquiring a long-term ability to launch attacks within the United States has been widely accepted as one of the group's main goals.