Sovereignty is generally defined as supreme, independent control and lawmaking authority over a territory. It is expressed through the power to rule and make law. Sovereignty entails hierarchy within a state as well as external autonomy, which refers to the ability of a state to act independently in international affairs. In any state, sovereignty is assigned to the person, body or institution that has the ultimate authority over its citizens and the power to modify existing laws. In political theory, sovereignty is a substantive term designating supreme legitimate authority over some polity.