Politics in the United States have long been dominated by a two-party system. But over the course of the nation's history, various groups at state and federal levels have tried to break into the system -- each supporting issues and views unrepresented by the dominant parties. Even barriers like the ballot access laws that make it difficult for third parties to get on a ticket haven't stopped these alternative parties from occasionally rising to the forefront.

In 2000, the Green Party was just such a group, nominating political activist and former independent candidate Ralph Nader for president. Nader ultimately took 2.7 percent of the popular vote in a race where a gap of only 0.5 percent separated Republican candidate George W. Bush from Democratic candidate Al Gore.

Due to this exposure and a growing state-level grassroots campaign, the Green movement continued to gain steam following the 2000 election. Running on such issues as environmental responsibility, nonviolence and global responsibility, the Greens currently boast 230 members in elected office throughout the U.S. and over 300,000 registered party members nationwide. The Greens have even managed to achieve ballot status in 20 states and the District of Columbia.

Third Parties and Presidential Races They say two's company, three's a crowd -- but why is American politics a two-party system? To a large extent, the country was born into the system as Federalists and Antifederalists argued over the U.S. Constitution. Since then, presidential elections usually pit two parties against each other. The U.S. uses a winner-takes-all or plurality system in elections -- the candidate with the most votes is the sole winner. This system encourages candidates to gravitate toward one party or the other. The Electoral College, campaign finance laws and ballot access laws also contribute to the dominance of the two party system. No third party candidate has ever taken the Whitehouse -- and only one man, George Washington, ever held the position as an independent.

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But where did the Green movement come from? What are its core values and where is it going? In this article, we'll answer each of these questions and get to the bottom of just how green politics work in the U.S.