Sovereignty is the claim to be the ultimate political authority, subject to no higher power as regards the making and enforcing of political decisions. In the international system, sovereignty is the claim by the state to full self‐government, and the mutual recognition of claims to sovereignty is the basis of international society. Sovereignty is the other side of the coin of international anarchy, for if states claim sovereignty, then the structure of the international system is by definition anarchic. Sovereignty should not be confused with freedom of action: sovereign actors may find themselves exercising freedom of decision within circumstances that are highly constrained by relations of unequal power.
The doctrine of sovereignty developed as part of the transformation of the medieval system in Europe into the modern state system, a process that culminated in the Treaty of Westphalia in 1648. In some ways the emergence of the concept of sovereignty ran parallel with the similar emergence of the idea of private property, both emphasizing exclusive rights concentrated in a single holder, in contrast to the medieval system of diffuse and many‐layered political and economic rights. Within the state, sovereignty signified the rise of the monarch to absolute prominence over rival feudal claimants such as the aristocracy, the papacy, and the Holy Roman Empire. Internationally, sovereignty served as the basis for exchanges of recognition on the basis of legal equality, and therefore as the basis of diplomacy and international law.
From: Iain McLean and Alistair McMillan, The Concise Oxford Dictionary of Politics (3rd ed.), Oxford University Press, 2009.