The first political parties in the United States emerged from the debate over the ratification of the Constitution in the 1780s. Those who supported ratification were known as Federalists and those opposed as the Anti-Federalists. The Federalists became the first real party and were led by Alexander Hamilton and John Adams. The party supported a strong central government and dominated the U.S. government from 1788 to 1800.

Thomas Jefferson founded the Democratic Republican Party to oppose the Federalists. The party emphasized individual rights and limitations on governmental power. Jefferson was elected president in 1800, and the party would control the White House for the next forty years. Although philosophically opposed to a strong central government, under the Democratic Republicans there was a gradual expansion of federal power.

Following the War of 1812 the nation entered a period dominated by personal politics. Jefferson's party split into factions, the National Republicans and the Democrats. The National Republicans were the more conservative faction and were led by John Quincy Adams and Henry Clay. The rival Democratic faction developed under the leadership of Andrew Jackson. These two blocs ultimately developed into distinct parties. The Adams-Clay group became the Whig Party and the Jacksonians became known simply as the Democratic Party, the oldest continuous political party in the world.

Although the Whigs were able to capture the White House twice, in 1840 with William Henry Harrison and in 1848 with Zachary Taylor, they became divided over the issue of slavery. The party's unity was tied more to opposition to the Democrats than to any common ideological base, and by the 1850s the Whigs began to break apart as a national party.

The demise of the Whigs led to the formation of a new party that was initially formed in opposition to slavery. The new Republican Party, or Grand Old Party (GOP), was established in 1854 and held its first national convention in 1856. With the formation of the GOP the modern two-party system in the United States was born.

With Abraham Lincoln's election in 1860, the Republicans began a period of substantive dominance of American politics. Reconstruction prevented most Southerners who had supported the Confederacy from voting and enfranchised African Americans, who voted overwhelmingly Republican. In the immediate postwar period Republicans gained state offices in the South for the first and only periods until the latter half of the twentieth century. This period was marked by the rise of regional politics as the North became overwhelmingly Republican and the South primarily Democratic after Reconstruction ended. During the period from 1860 to 1912, Grover Cleveland's two nonconsecutive terms (1885�1889 and 1893�1897) were the only times that Democrats were elected to the White House. However, by the late 1870s the Democrats had regained strength in both state offices and in Congress. Nonetheless, this period was marked by conservative, generally probusiness policies that emphasized industrialization at the national level.

In the latter half of the nineteenth century, popular dissatisfaction with both parties reached new heights. Political corruption was widespread, and both national parties developed powerful political machines. These organizations dominated politics at the local, state, and national levels and catered to the interests of elites. In the South, African Americans found themselves disenfranchised by Jim Crow laws, while industrial workers and immigrants in the North were exploited by factory bosses, and farmers in the Midwest and West were victimized by powerful railroad cartels. Throughout the country monopolies and trusts manipulated consumer prices.

In response to these problems a cross-party political movement, known as Progressivism, emerged. Progressivism spawned a number of third parties and forced the two national parties to adopt reformist positions. The assassination of Republican President William McKinley in 1901 led to the ascension of Theodore Roosevelt to the White House. The new president initiated a number of reforms and handpicked his successor, William Howard Taft, who was elected president in 1908. By 1912, however, Roosevelt believed that Taft had deviated from the Progressive policies that had marked the previous administration, and a major split developed in the GOP. Reformist members of the party supported Roosevelt in a third-party bid for the presidency after he was denied the opportunity to compete for the GOP nomination. Roosevelt and Taft split the Republican vote, allowing the Democratic candidate, Woodrow Wilson, to capture the presidency.

Wilson became the first Democratic president in twenty years. He served two terms, and under his leadership, substantial domestic reforms were enacted. However, Warren G. Harding's election in 1920 initiated twelve years of Republican control of the White House. The 1920s were dominated politically by a GOP that emphasized probusiness and limited-government policies. The nation's foreign policy was isolationist, and the economy of the nation was dominated by consumerism. The period is known as the era of "do-nothing presidents. "

The collapse of the U.S. economy and the onset of the Great Depression resulted in electoral disaster for the GOP. In 1932 the Democrats gained control of the White House and the House of Representatives. Since they already controlled the Senate, the elections gave Franklin D. Roosevelt and the Democrats control of the federal government. The new president used this power and his enormous personal appeal to enact the New Deal programs of domestic reforms, which dramatically expanded the size and scope of the national government. Roosevelt's election also ushered in a period of Democratic dominance of Congress, which lasted until the 1990s. The success of the party was based on Roosevelt's New Deal coalition, which brought together African Americans, Jewish Americans, Southern and rural whites, and the working class.

Roosevelt's successor, Harry Truman, endeavored to maintain the New Deal coalition through a domestic agenda known as the Fair Deal. Although the GOP captured the House in 1948, it would be the last time the party had a majority in that chamber until 1994. Republicans won the White House in 1952 on the strength of former general Dwight D. Eisenhower's personal popularity and a strong anti-Communist platform. From the Eisenhower administration onward, the GOP was able to portray itself as the party with stronger national defense policies.

The Democrats regained control of the White House in 1960, with the election of John F. Kennedy. After Kennedy's assassination Lyndon B. Johnson became president and endeavored to "complete" the New Deal with a series of domestic programs including Medicare. However, the civil rights movement and the Vietnam War led to a gradual breakdown of the New Deal coalition as rural whites and segments of the working class switched to the Republican Party. Richard M. Nixon capitalized on this trend with his "Southern strategy, " which emphasized law and order and traditional conservative values. The Watergate scandal ended the Nixon presidency and returned the Democrats to power following the 1976 election. Economic problems and global crises, such as the resurgence of the Soviet Union and the Iran hostage crisis, led to the election of Ronald Reagan in 1980.

Reagan's electoral success, which included Republican control of the Senate, was based on his neoconservative ideals, calling for reductions in the size and scope of government, and a renewed commitment to challenge the Soviet Union. The 1980 election also marked the emergence of the Christian Right as a significant force in American politics. Throughout the 1980s the GOP also gained strength in the South as previously Democratic strongholds began to break apart. Despite scandals in his second term, Reagan's popularity remained strong and his vice president, George H. Bush, won election in 1988. Bush concentrated on foreign policy, and while he was able to solidify the nation's position as the world's sole superpower, a domestic recession hurt his popularity. The candidacy of Ross Perot turned the 1992 presidential election into a three-way race in which the Democratic candidate, Bill Clinton, won the election. However, the Democrats lost nine seats in the House. The failure of several liberal initiatives, including a broad proposal to reform health care, led to a major reversal for the Democrats in the 1994 elections. The Republicans won majorities in both houses of Congress and won a majority of the nation's governorships. Clinton responded by adopting more conservative policies on welfare, immigration, and the scope of government. Clinton was reelected in 1996, although the GOP retained control of Congress. In 2000 Republican candidate George W. Bush won the presidency, the GOP retained control of the House, and the Senate was divided fifty-fifty.

With the Democrats becoming more centrist, the Republican Party has become more conservative. The Democratic Party has been hurt as its traditional base in the South has eroded; however, both parties have been weakened by two trends since World War II. The first is the gradual decline in party loyalty or affiliation. In 1940 some seventy-seven percent of Americans identified themselves as belonging to one of the two major parties. By 1995 that number had fallen to fifty-eight percent. The second trend is the common practice of voting for two or more parties in the same election (known as ticket-splitting). For instance, a voter will vote for one party's candidate for the presidency and a different party's candidate for the Senate. The practice of ticket-splitting may reflect a growing desire on the part of Americans for divided government in which different parties control the executive and the legislature.

Throughout American history there have been numerous third and minor parties that have influenced politics but have had limited success in the electoral arena. Even as party affiliation and ticket-splitting increase, the basic two-party system in the United States remains dominant.

One of the central reasons for the two-party system is historical. The early foundation of the political system in the United States was based on two opposing factions (the Federalists and the Anti-Federalists). This split reflected economic, ideological, and geographical divergences. The Federalists supported a strong central government and represented commercial interests such as merchants and manufacturers. The party was centered in the North. The Anti-Federalists were mainly farmers and workers, favoring states' rights and limited national government. The base of the Anti-Federalists was in the South.

By the time of the emergence of the Whig Party, the main ideological division pitted Eastern business interests against Southern and Western agricultural interests. The rise of the Republican Party marked the growing split between the North and the South over slavery, economics, and states' rights. The Republicans held sway in the North, while the Democrats dominated the South until the 1920s. During this period there was an ideological shift as the Democrats came to support a more significant role for the national government, while the GOP came to favor limited government.

The perpetuation of the two-party system is tied to the ability of the parties to make ideological shifts and to incorporate broad ideologies. The widespread sharing of core U.S. beliefs�such as private property and the free enterprise system�also reinforces the primacy of the two parties since alternative ideologies, such as socialism, have not had broad popular appeal. In addition, the separation of church and state has prevented the formation of minor religious parties. The two-party system has become part of the nation's political culture and is reinforced among young citizens through political socialization.

A major factor in the dominance of the two-party system is the winner-take-all electoral system. Since U.S. elections are decided by plurality from single-member districts, there is little chance for minor parties to be represented. This system is incorporated in the electoral college, in which the electors pledge to support candidates from their party. Voters, aware that minor parties have little chance under this system, are even less likely to vote for third parties. Contributors are also more likely to give financial assistance and campaign aid to existing parties. State and federal laws favor existing parties and make it more difficult for new parties to get candidates on the ballot. For instance, laws generally require new parties to get more signatures to place their candidate on the ballot than are required of existing parties.

A third party has never captured the White House, but in six of the eight presidential elections in which the minor parties have garnered more than ten percent of the popular vote, the incumbent party has lost the presidency. While third parties have not had much national success, they have been influential in gauging the nation's mood and expressing dissatisfaction with the major parties. This has forced the major parties to redefine policies and incorporate new issues. Although many third parties were founded for ideological reasons, the most successful were established by defectors from the major parties. These parties are known as spin-off parties.

Most often spin-off parties result when major figures in the established parties become dissatisfied or at odds with other leaders in the party. The best-known spin-off from the GOP is the Bull Moose Progressive Party of 1912. The party was founded by Theodore Roosevelt after he was denied the Republican nomination for the presidency. Roosevelt announced a progressive agenda that was far more radical than that of the GOP. Roosevelt received more votes than Taft, but they split the Republican vote so that the Democratic challenger, Woodrow Wilson, won the election.

The Democratic Party split in 1860 between the Democrats and the Southern Democrats. In the twentieth century there have been three major spin-off parties from the Democrats. The first two were the Dixiecrats (or States' Rights Party) and Henry Wallace's Progressive Party, both of 1948. The third was George Wallace's American Independent Party in 1968, which ran on a prosegregation platform and garnered 9.9 million popular votes and 46 electoral votes.

A number of single-issue parties have been formed. These include the Free Soil Party, which was formed in 1848 to oppose slavery; the Prohibition Party (1869), which advocated the abolition of alcohol; and the Greenback Party (1876), which was established to support paper money. The Populist Party advocated agrarian interests. In 1892 the party had its greatest success, winning one million popular votes and gaining 26 electoral votes. However, it aligned itself with the Democratic Party and, by 1908, it ceased to exist.

The Progressive Party was a prominent influence in American politics throughout the early twentieth century. The Progressives had their greatest success in the 1912 election and the 1924 election when they fielded Robert La Follette. A number of leftist parties were also formed near the turn of the twentieth century. The Socialist Party was the most successful of these parties and won over a thousand local elections; its perennial presidential candidate, Eugene V. Debs, ran for the presidency five times. On the Right, the Libertarian Party, formed in 1972, remains a prominent party, although one with little electoral success. The Reform Party of Ross Perot was formed in 1992, and its greatest success was the election of Jesse Ventura as governor of Minnesota. In addition, with consumer advocate Ralph Nader as a presidential candidate, the Green Party gained three percent of the vote in the 2000 election.