What idea is stated by "social contract" theory

Social contract theory, nearly as old as philosophy itself, is the view that persons' moral and/or political obligations are dependent upon a contract or agreement among them to form the society in which they live.

The idea that people join groups, and these groups make a presence known as a society; also the compact that the people agree from rules and conditions for membership in their society.

Explanation:

Locke viewed how people need to come together to make concessions to coexist.

In the natural state of man, a society can't develop, since the instincts of men are destructive, therefore are common will to come together and set rules and membership to form a government to secure rights for living together.

Since social relations agreed to chose their government, in any time the society is entitled to revoke its power, for citizens to withdraw their obligation to obey voluntarily, and change the leadership and its rulers-.