In the current environment, the threat of terrorism is a major shaping force of many nations’ international and domestic security policies. Nonstate groups with the intent and capability to take violent action are a reality in many countries given the existence of international movements, such as al Qaeda, that have the capacity to direct or inspire violence across the world, thereby creating another source of threat and risk. The threat of terrorist activity extends across a wide spectrum, from attacks causing little in the way of injury or damage to the potential for large-scale incidents. Although the probability of such high-consequence scenarios occurring is comparatively low, their ability to cause national-scale outcomes has meant that governments have focused their efforts on seeking to prevent them.
The core of government attempts to prevent violent and other criminal activity is intelligence and law enforcement, which, for many years, were viewed by Americans as separate activities. Put in place mainly to address the threat posed by agencies and agents of foreign governments, intelligence was viewed as an internationally focused activity that occurred largely outside U.S. borders. Intelligence agencies were charged with gathering information and learning about threats to the country, not prosecuting the perpetrators; these activities were designed to make it possible to take action to prevent attacks from happening. Law enforcement, in contrast, was done “at home” and, while certainly designed to help deter or prevent criminal activity, was largely a reactive enterprise. Law enforcement organizations, which generally did not act until after something had already happened, aimed to make