The following is a list of major political parties in the United States of America.
Current active parties
Formed after the Christian Democratic Party collapsed following the secession of the Republic of New England and Republic of the Pacific. The Conservative Party had initial success, but the "Socialist Decade" of the 1990s, after first Conservative president Jack Kemp invaded the RoP illegally, put it on hold. The Conservatives are generally seen as the strongest political party in the country, and is staunchly right wing.
The Socialist Party was founded in 1945 after the Democratic Party collapsed into the Socialists, Progressives and Moderates. Even though the Socialists and Progressives were no longer united under the Democratic Party banner, many Socialist candidates have been endorsed by Progressives and vice versa. The SP and PP have united for a presidential ticket a few times.
In 2003, the Socialist Party absorbed most of the Progressive Party. There are still some small Progressive parties in the United States, but they aren't really relevant.
The Socialists are significantly more center than their left-wing brethren across the world. This is seen as because of the United States' staunchly right wing political spectrum. They are generally received as the second strongest party in the country, and the only reason why Socialist Dennis Kucinich is in office is because of the disdain of Conservatives after the discovery of President Sarah Palin's illicit programs, and the Moderate's lack of a strong candidate.
One third of the remnant of the Democratic Party, the Moderates have always been the weakest of the three major parties. It has never had a successful Presidential candidate, only twice winning any electoral votes in a presidential election (1964 and 2000).
They have a few seats in congress, but have never done anything truly spectacular. While in the US they're seen as centrist, internationally they are actually center-right.
Prominent parties without representation
The Libertarian Party was founded in 1984, and is generally perceived as far-left socially and far-right fiscally. It advocates government out of the daily lives of people and out of business altogether. It appeals to some member of the Conservative Party who aren't necessarily socially conservative. While some elected CP members describe themselves as "libertarian", there has never been a member of the Libertarian Party elected to nationwide office.
Originally staunchly Conservative, during the Great Depression it moved to the left. After several defeats in elections, the party went it's separate ways, dissolving to the Moderate Party, Socialist Party and Progressive Party.
Founded in the 1860s as an anti-slavery party, with a left-leaning spin, it had moved solidly to the right by the time of it's collapse in the 1970s. The collapse of the "Grand Old Party (GOP)" was mainly due to the warring Christian and Moderate factions. After the GOP's collapse, the party split for either the Moderate Party, or the newly founded Christian Democratic Party in 1974.
Christian Democratic Party
Not related to the original Democratic Party, the CDP was founded as a place for hardcore Conservatives in 1969, but didn't achieve mainstream status until the Republican Party split in 1974. It had a short run in glory, however, as it collapsed in 1988 prior to the election of Jack Kemp to the presidency, in favor of the again newly founded Conservative Party.
Not related to Theodore Roosevelt's 1912 party of the same name, the Progressives were a group of center-left politicians who considered themselves too far left for the Moderate Party but too far center for the Socialist Party after the Democratic Party split in 1945. It had never had a successful presidential candidate and routinely endorsed Socialist candidates. It was relatively minor in 2003 when it was mostly absorbed into the Socialist Party.
Communist Party of America
The Communists were outlawed in 1958 as the Cold War with the communist Soviet Union was heating up. Afraid of a Communist coup by the CPA, far-right president Harry Byrd made illegal "Communist thought" in the McCarthy Amendment to the Constitution. There is still some underground Communist Parties, though the official one is inactive, and continually making its case to the Supreme Court for re-activation.
Green Party of the United States
Made illegal in 1991, just months after it was founded, the GPUS was thought to be a violation of the McCarthy Amendment. While most Americans opposed the McCarthy Amendment (and still do), the GPUS was made illegal in one of the final acts Jack Kemp made as President. It is much more likely to be reactivated under President Kucinich.
Workers' Party of the United States
The Workers' Party of the United States was banned under the McCarthy Amendment on June 14, 2010, just four months after it was founded and began having political events. A left-wing party, the Workers' Party had a few candidates going for municipal offices in big cities, but was banned and its members found for treason before the elections could even begin.