Information on the largest 5 for idiots!
The modern political party system in the United States is a two-party system dominated by the Democratic Party and the Republican Party. But other parties gained considerable recognition nationality the last few years. Here are the five largest.
Democratic Party

The Democratic Party is one of two major political parties in the United States. It is the oldest political party in the United States and among the oldest in the world.
The Democratic Party, since the division of the Republican Party in the election of 1912, has consistently positioned itself to the left of the Republican Party in economic as well as social matters. The economically left-leaning philosophy of Franklin D. Roosevelt, which has strongly influenced American liberalism, has shaped much of the party's economic agenda since 1932. Roosevelt's New Deal coalition usually controlled the national government until the 1970s. The civil rights movement of the 1960s has continued to inspire the party's liberal principles, despite having lost the more conservative South in the process.
Republican Party

The Republican Party is one of the two major contemporary political parties in the United States of America. It is often referred to as the Grand Old Party or the GOP.
Founded in 1854 by anti-slavery expansion activists and modernizers, Republican Party rose to prominence with the election of Abraham Lincoln, the first Republican president. The party presided over the American Civil War and Reconstruction and was harried by internal factions and scandals toward the end of the 19th century. Today, the Republican Party supports a conservative platform (as far as American politics are concerned), with further foundations in economic liberalism, fiscal conservatism, and social conservatism.
Constitution Party

The Constitution Party is a conservative United States political party. It was founded as the U.S. Taxpayers Party in 1992. The party's official name was changed to the Constitution Party in 1999; however, some state affiliate parties are known under different names.
According to ballot access expert Richard Winger, the editor of Ballot Access News, who periodically compiles and analyzes voter registration statistics as reported by state voter agencies, it ranks third nationally amongst all United States political parties in registered voters, with 366,937 registered members as of November 2006.
The Constitution Party advocates a platform that purports to reflect the Founding Fathers' original intent of the U.S. Constitution, principles found in the U.S. Declaration of Independence, and morals taken from the Bible.
Green Patry

In the United States, the Green Party has been active as a third party since the 1980s. The party first gained widespread public attention during Ralph Nader's presidential runs in 1996 and 2000. Currently, the primary national Green Party organization in the U.S. is the Green Party of the United States, which has eclipsed the earlier Greens/Green Party USA. There are Green Parties in many nations.
Libertarian Party

The Libertarian Party was founded on December 11, 1971. It is one of the largest continuing Third parties in the United States, claiming more than 200,000 registered voters and more than 600 people in public office, including mayors, county executives, county-council members, school-board members, and other local officials. It has more people in office than all other third parties combined.
The political platform of the Libertarian Party reflects that group's particular brand of libertarianism, favoring minimally regulated, laissez-faire markets, strong civil liberties, minimally regulated migration across borders, and non-interventionism in foreign policy that respects freedom of trade and travel to all foreign countries.
Reform Party

The Reform Party of the United States of America (abbreviated Reform Party USA or RPUSA, generally known simply as the Reform Party) is a political party in the United States, founded by Ross Perot in 1995 who said Americans were disillusioned with the state of politics—as being corrupt and unable to deal with vital issues—and desired a viable alternative to the Republican and Democratic Parties.
Its biggest victory came when Jesse Ventura was elected governor of Minnesota in 1998. Since then, the party has been fraught with infighting.