The world today is divided territorially into more than 190 countries, each of which possesses a national government that claims to exercise sovereignty and seeks to compel obedience to its will by its citizens. Governments can be classified in any number of ways. For example, they might be classified by the number of rulers, thus distinguishing government by one (as in a monarchy or a tyranny) from government by the few (in an aristocracy or oligarchy) and from government by the many (as in a democracy). Governments can also be classified by mode of succession; for example, ascension to governmental leadership may follow the rules of hereditary succession, or it may be determined through elections or by force. Governments also vary in terms of the laws and rules of conduct that each political entity follows.