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—from squads to companies and regiments, eventually to divisions and armies, as in Yugoslavia and China during the Second World War—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 operations is in the cities, and who have to operate clandestinely in small units. Any major concentration would immediately expose them to retaliation by the government. The terrorists may be part of a political movement that engages in propaganda and other political activities (such as the IRA and the Basque ETA), but there is a strict division of labor between the legal and the military arms of the movement.