The document discusses the differences between political parties and interest groups, as well as various aspects of the American political party system. It notes that political parties attempt to influence government by electing members to office and control the government, while interest groups seek to influence government on specific issues. It also discusses the history of American party systems, noting there have been four distinct systems, and how realignments have occurred when new parties replace old dominant ones. The document examines features of the US two-party system and electoral laws that promote two parties competing for the center of voters.