War (derived from middle latin wērra) is any large scale, violent conflict. War grows from the almost universal tribal warfare that has occurred throughout history, to wars between city states, nations, or empires. By extension, the word is now used for any struggle, as in the war on drugs or the war on terror. It was once thought man was the only animal who fought wars, but closer observation of animal life has discovered wars between ant colonies and chimpanzee tribes. A group of combatants and their support is called an army on land, a navy at sea, and air force at air. Wars may be prosecuted simultaneously in one or more different theatres. Within each theater, there may be one or more consecutive military campaigns. A military campaign includes not only fighting but also intelligence, troop movements, supplies, propaganda, and other components. Continuous conflict is traditionally called a battle, although this terminology is not always applied to conflicts involving aircraft, missiles or bombs alone, in the absence of ground troops or naval forces. A civil war is the use of force to resolve internal differences.