Terrorism
Terrorism is, in the broadest sense, the use of intentionally indiscriminate violence as a means to create terror among masses of people; or fear to achieve a religious or political aim. It is used in this regard primarily to refer to violence during peacetime or in war against non-combatants. The terms "terrorist" and "terrorism" originated during the French Revolution of the late 18th century but gained mainstream popularity during the U.S. presidency of Ronald Reagan (1981–89) after the 1983 Beirut barracks bombings and again after the 2001 September 11 attacks and the 2002 Bali bombings.
Foreign internal defense
Insurgency matters today because it is linked to the phenomenon of transnational terrorism. Insurgents have long used terrorism in the operational sense, deterring those who supported the government and creating an environment of violence and insecurity to erode public trust in the regime. But now terrorism plays a strategic role as well. Insurgents can use terrorism as a form of long-range power projection against outsiders who support the government they are fighting. This could deter or even end outside assistance. It is easy to imagine, for instance, that the already fragile backing for American involvement in Iraq would erode even further if the Iraqi insurgents launched attacks in the United States. Even more important, an insurgent movement able to seize control of a state could support transnational terrorists. The idea is that insurgents have demonstrated an affinity for violence and extremism which would flavor their policies if they came to power.