In sociology and biology, conflict theory states that the society or organization functions so that each individual participant and its groups struggle to maximize their benefits, which inevitably contributes to social change such as changes in politics and revolutions. The theory is mostly applied to explain conflict between social classes in ideologies such as socialism and communism. The theory refutes functionalism, which considers that societies and organization function so that each individual and group plays a specific role, like organs in the body. There are radical basic assumptions (it is only conflict, which might explain social change), or moderate ones (custom and conflict are always mixed).

In understanding conflict theory, competition plays a key part.

The following are four primary assumptions of modern conflict theory:

1. Competition. Competition over scarce resources (money, leisure, sexual partners, and so on) is at the heart of all social relationships. Competition rather than consensus is characteristic of human relationships.
2. Structural inequality. Inequalities in power and reward are built into all social structures. Individuals and groups that benefit from any particular structure strive to see it maintained.
3. Revolution. Change occurs as a result of conflict between competing interests rather than through adaptation. It is often abrupt and revolutionary rather than evolutionary.
4. War. Even war is a unifier of the societies involved, as well as war may set an end to whole societies.

Conflict theory was elaborated e. g. in the United Kingdom by Max Gluckman and John Rex , in the United States by Lewis A. Coser and Randall Collins , and in Germany (later the United Kingdom) by Ralf Dahrendorf, all of them being less or more influenced by Karl Marx, Ludwig Gumplovicz, Vilfredo Pareto, Georg Simmel, and other founder fathers of European sociology.

See also Important publications in conflict theory