But, as Carl von Clausewitz stressed, the whole effort in war—at least in non‐criminal ones—is to obtain political goals. In his most famous formulation, “war is a mere continuation of policy with other means” and is “a true political instrument.” And the means to attaining that goal, stresses Clausewitz, involve using coercion and inflicting fear and intimidation to break the enemy’s will—that is, to create “compliant behavior.” In battle, says Clausewitz, “the loss of morale” is the “major decisive factor.”
Wars, then, do not involve the annihilation of the enemy, but the breaking of the enemy’s will, something that sometimes comes quite quickly and sometimes, as happened to the United States in Vietnam, only after long episodes of attrition.
Focusing only on violence against civilians does not really make for a helpful distinction between war and terrorism. Some terrorist campaigns seek to avoid civilian casualties as do some military ones. However, many of each variety kill civilians either as an incidental result of violence or through direct intent. As legal national security expert Matthew Waxman points out, the “punishment of civilians is a commonly used strategy of coercion” in warfare.
Terrorism differs from war, and particularly from insurgency, not in its essential method or goal or in the targets of violence, but in the frequency with which violence is committed.
Before 9/11, terrorism was, by definition, a limited phenomenon. It was often called the “weapon of the weak” because it inflicted damage only sporadically. If terroristic violence became really sustained and extensive in an area—if it was no longer fitful or sporadic—the activity was generally no longer called terrorism, but rather war or insurgency.
Thus, the Irish Republican Army was commonly taken to be a terrorist enterprise, while fighters in Sri Lanka in the 1990s were considered to be combatants in a civil war situation. And in the early and middle 1960s, the Vietnamese Communists’ campaign of assassination, ambush, harassment, sabotage, and assault was generally considered insurgent or guerrilla war, not terrorism, because violence was so sustained — even though its campaign included acts of violence against civilians that were often essentially random.