The Terrorist Enemy

Terrorist networks currently pose the greatest national security threat to the United States. The greatest threat and the most wanted terrorists come from the al-Qaida (AQ) network, which includes a core al-Qaida organization and numerous confederated extremist groups.

The al-Qaida network has many of the characteristics of a "globalized insurgency" and employs subversion, sabotage, open warfare and, of course, terrorism. It seeks weapons of mass destruction or other means to inflict massive damage on the United States, our allies and interests, and the broader international system. AQ aims to overthrow the existing world order and replace it with a reactionary, authoritarian, transnational entity. This threat will be sustained over a protracted period (decades not years) and will require a global response executed regionally, nationally, and locally.

via state.gov

If you are interested in the U.S. Government's views on terrorism, this article is good reading.