The evolution of state formation criteria: from effectiveness to legitimacy?

States are one of the main subjects of international law. There is no all-agreed definition for the concept of state. The only document that defines the elements of state is the Montevideo Convention on the Rights and Duties of States, known as Montevideo Convention 1933, in which a State as a person of international law should possess the following qualifications: (a) a permanent population; (b) a defined territory; (c) government; and (d) capacity to enter into relations with other states. There is no agreement on the limits and ambit of such traditional qualifications. The increase in the number of states, especially in the second half of the twentieth century onward, with the absence of some of the above qualifications, indicates the formation of new criteria based on legality and legitimacy. Such novel qualifications are jus cogens rules of international law, including the formation of new states based on the “right of self-determination” and the principle of the prohibition of “use of force’.