A monarchy is a kind of government where a monarch, a kind of hereditary ruler (someone who inherits their office), is the head of state. Monarchs usually rule until they die or pass down (when a monarch resigns it is called abdication). Most monarchies are hereditary, but some are elected. The most famous elected monarch is the Pope of the Roman Catholic Church. Some well known titles for monarchs are King, Queen, Emperor, Empress, Czar, Kaiser, Shah, Emir, Khan and Sultan.
In less formal societies, the leader was often chosen by fighting. That was the way of warrior societies like the Zulu. Kings of England and Scotland were sometimes decided by battle. Warfare has been very frequent between human societies. "Wars of succession" is the general term for warfare caused by two or more individuals claiming the right of successor to a dead or deposed monarch.