Waging war using irregular forces fighting small-scale limited actions, usually in conjunction with a larger political and military strategy, against orthodox military forces. Guerrillas are usually nondescript in dress, heterogeneous in weapons and equipment, lack formal supply lines and employ highly unorthodox tactics. In addition to highly mobile, aggressive operations, these tactics embrace all aspects of psychological warfare, including the use of sabotage and terrorism.
Throughout history invading armies have been harassed by bands of guerrillas. These small mobile units were given their name during the Napoleonic War in Spain, and were often an adjunct to the national army. Today urban guerrillas often employ terror tactics.
Guerrilla warfare is employed when an invading army or occupying power fails to meet the expectations of those people whom they control or govern. The guerrilla must gain the support of the masses on whose behalf they are fighting as well as to increase their numbers. Guerrillas have been known to gain support by appealing to patriotism, to the hope of quick money and power and to terror or threats, to name a few.
The essence of guerrilla warfare is to establish foci, or liberated areas, in the countryside and to set up small military units which will gradually grow in strength, number and equipment, in order to fight battles against government troops. In the liberated areas, the guerrillas establish their own institutions, conduct propaganda and engage in other open political activities. None of this applies to terrorists, whose base of operation is in the cities, and who have to operate clandestinely in small units.
Guerrilla war is described as a prolonged war of attrition, with progressively increasing violence, blurred limits, a fluid line of contact, emphasizing the human factor. In the course of the war, guerrilla combatants become regular military forces until victory is attained and one party is defeated.
Often the continued and unrelenting activities of guerrilla bands destroy any possibility of political solution to the issue being fought over.