Political parties have shifted many times in 220 years of national politics. Even when parties have kept the same names for long periods, their issues, principles, demographics, and regional support all change over time.

The attached resources show and discuss the evolution of political party systems in the U.S. from 1820 to 1860. Each "party system" is a roughly defined time period in which two major political parties, each with fairly consistent supporters and beliefs, dominated the political scene. The colored lines represent organized parties that had a significant impact on national politics, electing members of Congress or receiving more than 1% of the vote for President. Where the lines merge and split, parties split or party affiliations changed dramatically in a short period of time. Presidential candidates are also listed for each party.