Use this American Government by the People video entitled Interest Groups: The Politics of Influence to understand how government works and to study how interest groups exist to make demands on government. The dominant interest groups in the United States are economic or occupational, but a variety of other groups--ideological, public interest, foreign policy, government itself, and ethnic, religious, and racial--have memberships that cut across the big economic groupings; thus, their influence is both reduced and stabilized.
Learn about Interest Groups and The Politics of Influence.