"A Military Guide to Terrorism in the Twenty-First Century" is a reference guide prepared under the direction of the U.S. Army Training and Doctrine Command (TRADOC), TRADOC G2 as a capstone reference guide on terrorism. TRADOC G2 Handbook No. 1, A Military Guide to Terrorism in the Twenty-First Century is prepared by the TRADOC Intelligence Support Activity (TRISA)-Threats. Understanding terrorism spans foreign and domestic threats of nation-states, rogue states with international or transnational agents, and other actors with specific strategies, tactics, and targets. This terrorism guide addresses foreign and domestic threats against the United States of America in a contemporary operational environment (COE). This informational handbook supports institutional training, professional military education, and operational missions for U.S. military forces in the War on Terrorism (WOT). This document provides an introduction to the nature of terrorism and recognition of terrorist threats to U.S. military forces. A common situational awareness by U.S. military forces considers three principal venues for armed forces: forces that are deployed, forces that are in transit to or from an operational mission, and forces that are primarily installation or institution support. Compiled from open source materials, this handbook promotes a "Threats" perspective and enemy situational awareness of U.S. strategies and operations in combating terrorism. Neither a counterterrorism directive nor antiterrorism manual, this handbook complements but does not replace Army training and intelligence products on terrorism.