Member states of the United Nations, all of which are sovereign states.
A sovereign state is a nonphysical juridical entity of the international legal system that is represented by a centralized government that has supreme independent authority over a geographic area. International law defines sovereign states as having a permanent population, a government, and the capacity to enter into relations with other sovereign states. It is also normally understood to be a state which is neither dependent on nor subject to any other power or state. The existence or disappearance of a state is a question of fact. While according to the declarative theory of state recognition a sovereign state can exist without being recognised by other sovereign states, unrecognised states will often find it hard to exercise full treaty-making powers and engage in diplomatic relations with other sovereign states.
The first states came into existence as people "gradually transferred their allegiance from an individual sovereign (king, duke, prince) to an intangible but territorial political entity, of the state". States are but one of several political orders that emerged from feudal Europe (others being city states, leagues, and empires with universalist claims to authority.
Westphalian sovereignty is the concept of nation-state sovereignty based on territoriality and the absence of a role for external agents in domestic structures. It is an international system of states, multinational corporations, and organizations that began with the Peace of Westphalia in 1648.
Sovereignty is a term that is frequently misused. Up until the 19th century, the radicalised concept of a "standard of civilisation" was routinely deployed to determine that certain peoples in the world were "uncivilised", and lacking organised societies. That position was reflected and constituted in the notion that their "sovereignty" was either completely lacking, or at least of an inferior character when compared to that of "civilised" people."Lassa Oppenheim said "There exists perhaps no conception the meaning of which is more controversial than that of sovereignty. It is an indisputable fact that this conception, from the moment when it was introduced into political science until the present day, has never had a meaning which was universally agreed upon." In the opinion of H. V. Evatt of the High Court of Australia "sovereignty is neither a question of fact, nor a question of law, but a question that does not arise at all." 
Sovereignty has taken on a different meaning with the development of the principle of self-determination and the prohibition against the threat or use of force as jus cogens norms of modern international law. The United Nations Charter, the Draft Declaration on Rights and Duties of States, and the charters of regional international organisations express the view that all states are juridically equal and enjoy the same rights and duties based upon the mere fact of their existence as persons under international law. The right of nations to determine their own political status and exercise permanent sovereignty within the limits of their territorial jurisdictions is widely recognised.
In political science, sovereignty is usually defined as the most essential attribute of the state in the form of its complete self-sufficiency in the frames of a certain territory, that is its supremacy in the domestic policy and independence in the foreign one.
In casual usage, the terms "country", "nation", and "state" are often used as if they were synonymous; but in a more strict usage they can be distinguished:
Nation denotes a people who are believed to or deemed to share common customs, religion, language, origins, ancestry or history. However, the adjectives national and international are frequently used to refer to matters pertaining to what are strictly sovereign states, as in national capital, international law.
State recognition signifies the decision of a sovereign state to treat another entity as also being a sovereign state. Recognition can be either express or implied and is usually retroactive in its effects. It doesn't necessarily signify a desire to establish or maintain diplomatic relations.
There is no definition that is binding on all the members of the community of nations on the criteria for statehood. In actual practice, the criteria are mainly political, not legal. L.C. Green cited the recognition of the unborn Polish and Czech states in World War I and explained that "since recognition of statehood is a matter of discretion, it is open to any existing State to accept as a state any entity it wishes, regardless of the existence of territory or of an established government."
In international law, however, there are several theories of when a state should be recognized as sovereign.
The constitutive theory of statehood defines a state as a person of international law if, and only if, it is recognized as sovereign by other states. This theory of recognition was developed in the 19th century. Under it, a state was sovereign if another sovereign state recognized it as such. Because of this, new states could not immediately become part of the international community or be bound by international law, and recognized nations did not have to respect international law in their dealings with them. In 1815 at the Congress of Vienna the Final Act recognised only 39 sovereign states in the European diplomatic system, and as a result it was firmly established that in future new states would have to be recognized by other states, and that meant in practice recognition by one or more of the great powers.
One of the major criticisms of this law is the confusion caused when some states recognize a new entity, but other states do not. Hersch Lauterpacht, one of the theory's main proponents, suggested that it is a state's duty to grant recognition as a possible solution. However, a state may use any criteria when judging if they should give recognition and they have no obligation to use such criteria. Many states may only recognize another state if it is to their advantage.
...International Law does not say that a State is not in existence as long as it isn't recognised, but it takes no notice of it before its recognition. Through recognition only and exclusively a State becomes an International Person and a subject of International Law.
By contrast, the "declarative" theory defines a state as a person in international law if it meets the following criteria: 1) a defined territory; 2) a permanent population; 3) a government and 4) a capacity to enter into relations with other states. According to declarative theory, an entity's statehood is independent of its recognition by other states. The declarative model was most famously expressed in the 1933 Montevideo Convention.
Article 3 of the Montevideo Convention declares that statehood is independent of recognition by other states. In contrast, recognition is considered a requirement for statehood by the constitutive theory of statehood.
State practice relating the recognition states typically falls somewhere between the declaratory and constitutive approaches. International law does not require a state to recognise other states.
Recognition is often withheld when a new state is seen as illegitimate or has come about in breach of international law. Almost universal non-recognition by the international community of Rhodesia and Northern Cyprus are good examples of this. In the former case, recognition was widely withheld when the white minority seized power and attempted to form a state along the lines of Apartheid South Africa, a move that the United Nations Security Council described as the creation of an "illegal racist minority régime". In the latter case, recognition was widely withheld from a state created in Northern Cyprus on land illegally invaded by Turkey in 1974.
Although the terms "state" and "government" are often used interchangeably, international law is predicated on a distinction between nonphysical states and their governments, and in fact, the concept of "government-in-exile" is predicated upon the distinction between states and their governments. States are nonphysical juridical entities, and not organizations of any kind, though, ordinarily, only the government of a state is allowed to obligate or bind it, for example by treaty.
Generally speaking, states are durable entities, though it is possible for them to be become extinguished, either through voluntary means or by military conquest. Because states are nonphysical juridical entities, their extinction cannot be due to only physical force alone. Instead the physical actions of the military must be associated with the correct social or judiciary actions in order to abolish a state.
Shaw, Malcolm Nathan (2003). International law. Cambridge University Press. p. 178. "Article 1 of the Montevideo Convention on Rights and Duties of States, 1933 lays down the most widely accepted formulation of the criteria of statehood in international law. It note that the state as an international person 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'"
Jasentuliyana, Nandasiri, ed. (1995). Perspectives on international law. Kluwer Law International. p. 20. "So far as States are concerned, the traditional definitions provided for in the Montevideo Convention remain generally accepted."
Wheaton, Henry (1836). Elements of international law: with a sketch of the history of the science. Carey, Lea & Blanchard. p. 51. "A sovereign state is generally defined to be any nation or people, whatever may be the form of its internal constitution, which governs itself independently of foreign powers."
"sovereign", The American Heritage Dictionary of the English Language (4th ed.) (Houghton Mifflin Company), 2004, retrieved 21 February 2010, "adj. 1. Self-governing; independent: a sovereign state."
^Glassner, Martin Ira; Fahrer, Chuck (2004). Political Geography (3rd ed.). Hoboken: Wiley. p. 14. ISBN0-471-35266-7.
^Spruyt, H. (1994). The Sovereign State and its Competitors: An Analysis of Systems Change. Princeton, NJ: Princeton University Press. ISBN0-691-03356-0.
^Krasner, Stephen D. (1999). Sovereignty: Organized Hypocrisy. Princeton University Press. ISBN0-691-00711-X.
^Wilde, Ralph (2009). "From Trusteeship to Self-Determination and Back Again: The Role of the Hague Regulations in the Evolution of International Trusteeship, and the Framework of Rights and Duties of Occupying Powers". Loy. L.A. Int'l & Comp. L. Rev.31: 85–142 [p. 94].
^Lassa Oppenheim, International Law 66 (Sir Arnold D. McNair ed., 4th ed. 1928)
^Akweenda, S. (1997). "Sovereignty in cases of Mandated Territories". International law and the protection of Namibia's territorial integrity. Martinus Nijhoff Publishers. p. 40. ISBN90-411-0412-7.
^ abStaff writers (20 February 2008). "Palestinians 'may declare state'". BBC News (British Broadcasting Corporation). Retrieved 2011-01-22.:"Saeb Erekat, disagreed arguing that the Palestine Liberation Organisation had already declared independence in 1988. "Now we need real independence, not a declaration. We need real independence by ending the occupation. We are not Kosovo. We are under Israeli occupation and for independence we need to acquire independence".
^Israel's Disengagement Plan: Renewing the Peace Process: "Israel will guard the perimeter of the Gaza Strip, continue to control Gaza air space, and continue to patrol the sea off the Gaza coast. ... Israel will continue to maintain its essential military presence to prevent arms smuggling along the border between the Gaza Strip and Egypt (Philadelphi Route), until the security situation and cooperation with Egypt permit an alternative security arrangement."