Since 1960 the number of interest groups has increased rapidly. There have been other historical eras of interest group proliferation. Interest groups do not, therefore, arise spontaneously or automatically out of natural social processes. At least four factors help explain the rise of interest groups. Broad economic developments.
Public programs create constituencies with an incentive to organize to maintain their benefits.
Sometimes government policies are designed to make private interest group formation easier, as was the case with the passage of laws in the 1930s to aid labor. Religious and moralistic movements. These produce people, frequently young people, who are willing to form organizations, often at large personal cost. The religious revivals of the 1830s and 1840s thus fed the antislavery crusade, and the civil rights and antiwar movements of the 1960s likewise produced an organizational explosion. The more activities government undertakes, the more interest groups form as a response to those activities.