State of nature
The state of nature is a term in political philosophy used in social contract theories to describe the hypothetical condition that preceded governments. There must have been a time before government, and so the question is how legitimate government could emerge from such a starting position, and what are the hypothetical reasons for entering a state of society by establishing a government.
In some versions of social contract theory, there are no rights in the state of nature, only freedoms, and it is the contract that creates rights and obligations. In other versions the opposite occurs: the contract imposes restrictions upon individuals that curtail their natural rights.
The time-period before the establishment of government, which political philosophers call the "state of nature," however, is regarded in the modern scientific era not only as hypothetical but actual. Societies existing before or without a political state are currently studied in such diverse fields as paleolithic history, archaeology, cultural anthropology, social anthropology, and ethnology, which investigate the social and power-related structures of indigenous and uncontacted peoples living in tribal communities.
Thomas Aquinas' theology 
The term "state of nature" appears in the writings of Thomas Aquinas (born c. 1225) (see De Veritate, Question 19, Article 1, Answer 13). Aside from its influence upon later Political Philosophy, the use of the term in Aquinas is also of key importance for the development of the Catholic "Natural Law" Theological Tradition; its biblical theological provenance goes back to a pregnant statement of the Apostle Paul in his Letter to the Romans (Romans 2:12-16).
For Paul, in Romans chapter 2, the "natural law" is contrasted with the Mosaic Law posited on Mount Sinai in that the Jewish Nation possessed the latter while the Gentile Nations lacked the Law of Moses but possessed the former in virtue of knowing (some of its central commandments) and obeying it (partially) "by nature." From this theological interpretation (one now controversial among leading Paulinists, i.e., it is disputed that Paul actually intended all of the later machinery of the "Natural Law" tradition) it was but a small step to speak of this perceived natural condition of the Gentile Nations (i.e., their "natural" nomological condition) as a "state of nature."
However, for Aquinas, following Aristotle, the State of Nature is not logically (or temporally) prior to the politically constituted community but is that community, i.e. for both Aristotle and Aquinas the political state is natural for human beings (see Encyclopedia of Political Theory, by Mark Bevin, s.v., "Thomism, "Natural Law"). In later Political Philosophy (e.g., Hobbes and Locke) the (hypothetical if not temporal) positing of the priority of the State of Nature will become a standard move.
Aquinas also employed the terms "primitive state" (statum primi) and "state of innocence" (statu innocentiae) (see Summa Theologica, Part I, Question 97, "Of the Preservation of the Individual in the Primitive State").
Thomas Hobbes 
The pure state of nature or "the natural condition of mankind" was deduced by the 17th century English philosopher Thomas Hobbes, in Leviathan and in his earlier work On the Citizen. Hobbes argued that all humans are by nature equal in faculties of body and mind (i.e. no natural inequalities are so great as to give anyone a "claim" to an exclusive "benefit"). From this equality and other causes in human nature, everyone is naturally willing to fight one another: so that "during the time men live without a common power to keep them all in awe, they are in that condition which is called war; and such a war as is of every man against every man". In this state every person has a natural right or liberty to do anything one thinks necessary for preserving one's own life; and life is "solitary, poor, nasty, brutish, and short" (Leviathan, Chapters XIII-XIV). Hobbes described this natural condition with the Latin phrase bellum omnium contra omnes (meaning war of all against all), in his work De Cive.
Within the state of nature there is neither personal property nor injustice since there is no law, except for certain natural precepts discovered by reason ("laws of nature"): the first of which is "that every man ought to endeavour peace, as far as he has hope of obtaining it" (Leviathan, Ch. XIV); and the second is "that a man be willing, when others are so too, as far forth as for peace and defence of himself he shall think it necessary, to lay down this right to all things; and be contented with so much liberty against other men as he would allow other men against himself" (loc. cit.). From here Hobbes develops the way out of the state of nature into political society and government, by mutual contracts.
According to Hobbes the state of nature exists at all times among independent countries, over whom there is no law except for those same precepts or laws of nature (Leviathan, Chapters XIII, XXX end). His view of the state of nature helped to serve as a basis for theories of international law and realism.
Locke's view on the state of nature 
John Locke considers the state of nature in his Second Treatise on Civil Government written around the time of the Exclusion Crisis in England during the 1680s. For Locke, in the state of nature all men are free "to order their actions, and dispose of their possessions and persons, as they think fit, within the bounds of the law of nature." (2nd Tr., §4). "The state of Nature has a law of Nature to govern it", and that law is Reason. Locke believes that reason teaches that "no one ought to harm another in his life, liberty, and or property"; and that transgressions of this may be punished. This view of the state of nature is partly deduced from Christian belief (unlike Hobbes, whose philosophy is not dependent upon any prior theology).
Although it may be natural to assume that Locke was responding to Hobbes, Locke never refers to Hobbes by name, and may instead have been responding to other writers of the day, like Robert Filmer. In fact, Locke's First Treatise is entirely a response to Filmer's Patriarcha, and takes a step by step method to refuting Filmer's theory set out in Patriarcha. The conservative party at the time had rallied behind Filmer's Patriarcha, whereas the Whigs, scared of another prosecution of Anglicans and Protestants, rallied behind the theory set out by Locke in his Two Treatises of Government; as it gives a clear theory as to why you should be allowed to overthrow a monarchy who abuses the trust set in it by the people.
Hobbes's view was challenged in the eighteenth century by Jean-Jacques Rousseau, who claimed that Hobbes was taking socialized people and simply imagining them living outside of the society in which they were raised. He affirmed instead that people were neither good nor bad. In Rousseau's state of nature, people did not know each other enough, and they did have normal values. The modern society is blamed for blemishing the pure people.
Hume's theory 
David Hume offers in A Treatise of Human Nature (1739), that human beings are naturally social: "’Tis utterly impossible for men to remain any considerable time in that savage condition, which precedes society; but that his very first state and situation may justly be esteem’d social. This, however, hinders not, but that philosophers may, if they please, extend their reasoning to the suppos’d state of nature; provided they allow it to be a mere philosophical fiction, which never had, and never cou’d have any reality." (Book III, Part II, Section II: "Of the Origin of Justice and Property."
Hume's ideas about human nature expressed in the Treatise suggest that he would be happy with neither Hobbes's nor his contemporary Rousseau's thought-experiments. He explicitly derides as incredible the hypothetical humanity described in Hobbes's Leviathan (Book II, Part III, Section I: "Of Liberty and Necessity"). And he argues in "Of the Origin of Justice and Property" that if mankind were universally benevolent, we would not hold Justice to be a virtue: "’tis only from the selfishness and confin’d generosity of men, along with the scanty provision nature has made for his wants, that justice derives its origin."
20th century 
John Rawls used what amounted to an artificial state of nature. To develop his theory of Justice, Rawls places everyone in the original position. The original position is a hypothetical state of nature used as a thought experiment to develop Rawls' theory of justice. People in the original position have no society and are under a veil of ignorance that prevents them from knowing how they may benefit from society. They lack foreknowledge of their intelligence, wealth, or abilities. Rawls reasons that people in the original position would want a society where they had their basic liberties protected and where they had some economic guarantees as well. If society were to be constructed from scratch through a social agreement between individuals, these principles would be the expected basis of such an agreement. Thus, these principles should form the basis of real, modern societies since everyone should consent to them if society were organized from scratch in fair agreements.
Rawls's Harvard colleague Robert Nozick countered the liberal A Theory of Justice with a libertarian Anarchy, State, and Utopia, also grounded in the state of nature tradition. Nozick argued that a minimalist state of property rights and basic law enforcement would develop out of a state of nature without violating anyone's rights or using force. Mutual agreements among individuals rather than social contract would lead to this minimal state.
Between nations 
In Hobbes's view, once a civil government is instituted, the state of nature has disappeared between individuals because of the civil power which exists to enforce contracts and the laws of nature generally. Between nations, however, no such power exists and therefore nations have the same rights to preserve themselves - including making war - as individuals possessed. Such a conclusion led some writers to the idea of an association of nations or worldwide civil society. Among them there were Immanuel Kant with his work on perpetual peace.
Rawls also examines the state of nature between nations. In his work the Law of Peoples, Rawls applies a modified version of his original position thought experiment to international relationships. Rawls says that people, not states, form the basic unit that should be examined. States should be encouraged to follow the principles from Rawls's earlier Theory of Justice. Democracy seems like it would be the most logical means of accomplishing these goals, but benign non-democracies should be seen as acceptable at the international stage. Rawls develops eight principles for how people should act on an international stage.
- Hobbes, Thomas, Leviathan. 1651. Edwin Curley (Ed.) 1994. Hackett Publishing.
- Skinner, Quentin Visions of Politics. Cambridge.
- Rothbard, Murray N. "Robert Nozick and the Immaculate Conception of the State." Journal of Libertarian Studies. Vol 1, Num 1., pp45-47. 1977. http://mises.org/journals/jls/1_1/1_1_6.pdf