A State is usually defined as an entity with a monopoly on the legitimate use of force within a defined territory. "Legitimate" can be understood as meaning that the use of force by the State is widely accepted by the public both inside and outside the State's territory, even if acceptance is not universal.
 Philosophies of the state
Different political philosophies have distinct opinions concerning the state as a domestic organization monopolizing force. In the modern era, these philosophies emerged with the rise of capitalism, which coincided with the (re)emergence of the state as a separate and centralized sector of society. Philosophers such as Thomas Hobbes, John Locke, and Jean-Jacques Rousseau pondered issues concerning the ideal and actual roles of the state. Nowadays, there are four major philosophies of the state: anarchism, conservatism, liberalism, and Marxism.
Several of these philosophies use one form or another of the social contract theory, which affirms that the role of the state is (or should be) to follow the will of the people and serve their interests, as they define them.
In anarchist thinking, the state is nothing but an unnecessary and exploitative segment of society. Totally rejecting Hobbesian ideas, anarchists argue that if the state and its restrictions on individual freedom were abolished, people could figure out how to work together peacefully -- while individual creativity would be unleashed. Also rejecting the Marxist perspective, the anarchists hope that the withering away of the state can and will precede -- or coincide with -- the abolition of non-state forms of domination.
In some conservative thinking, the existing structure of tradition and hierarchies (of class, patriarchy, ethnic dominance, etc.) are seen as benefiting society overall. Thus, in a way, these conservatives accept some ideas from both the Marxist and the liberal schools of thought, but view them in a different light: the state forces people to accept class and other kinds of domination, but this is seen as being good for them. (They are like free-riders if they rebel.) Further, as with the liberals, the state is seen as always existing and/or "natural." "Withering away" will never happen.
In broadly-defined liberal thinking, the state should express the public interest, the interests of the whole society, and to reconcile that with those of individuals. (This job seems best performed by a democratically-controlled state, but different types of liberalism put different meanings on the word "democracy.") The state provides public goods and other kinds of collective consumption, while preventing individuals from free-riding (taking advantage of collective consumption without paying) by forcing them to pay taxes.
Within this school, there is a wide variety of differences of opinion, varying from free-market libertarianism to modern, New Deal, or social liberalism. The main debate along this line concerns the ideal size and role of the state. While libertarians argue for a small or "minimal" state, which simply protects property rights and enforces individual contracts, the New Deal or social liberals argue that the state has a greater positive role to play, given the problems of market failure and gross inequalities in the distribution of income and wealth inside a capitalist system. In general, almost no liberals see the state as currently living up to the philosophical ideal, and therefore argue for change in one direction or another.
In the Marxist school of thought, the main role of the state in practice is to use force to defend the existing system of class domination and exploitation. Under such systems as feudalism, the lords used their own military force to exploit their vassals. Under capitalism, on the other hand, the use of force is centralized in a specialized organization which protects the capitalists' class monopoly of ownership of the means of production, allowing the exploitation of those without such ownership. In modern Marxian theory, such class domination can coincide with other forms of domination (such as patriarchy and ethnic hierarchies).
Further, in Marxist theory, classes and other forms of exploitation should be abolished by establishing a socialist system, which must involve a democratic state. This state will then slowly "wither away" as the people take more and more power in their own hands and representative democracy slowly transforms into direct democracy. Once the process is complete, the communist social order has been achieved and the state no longer exists as an entity separate from the people. Thus, the ideal condition of the state in Marxist theory is the same as in anarchist theory: ideally, the state would not exist at all.