The view that a political system is healthiest when power is dispersed among many competing groups and interests, rather than concentrated in a single centre; also, the fact of diversity of values and groups.
In more detail
Robert Dahl's A Preface to Democratic Theory (1956) and Who Governs? (1961) are classic statements of the interest-group pluralist account of American politics. Critics argue that pluralism understates inequalities of organisation and resources, and that business and other groups hold structural advantages.