The need to win popular support in a
republic led to the American invention of voter-based political parties in the 1790s.
 Americans were especially innovative in devising new campaign techniques that linked public opinion with public policy through the party.
Political scientists and historians have divided the development of America's two-party system into five eras.
 The first two-party system consisted of the
Federalist Party, who supported the ratification of the Constitution, and the
Democratic-Republican Party or the Anti-Federalists, who opposed the powerful central government, among others, that the Constitution established when it took effect in 1789.
The modern two-party system consists of the
Democratic Party and the
Republican Party. Several
third parties also operate in the U.S., and from time to time elect someone to local office.
 The largest third party since the 1980s is the
Besides the Constitution, Green, and Libertarian parties, there are
many other political parties that receive only minimal support and only appear on the ballot in one or a few states.
Some political candidates, and many voters, choose not to identify with a particular political party. In some states,
independents are not allowed to vote in primary elections, but in others, they can vote in any primary election of their choice. Although the term "independent" often is used as a synonym for "moderate," "centrist," or "swing voter," to refer to a politician or voter who holds views that incorporate facets of both liberal and conservative ideologies, an independent can be of any ideological or political persuasion.