William H. Seward
The Republican Party had been founded in 1854, in reaction to the Kansas-Nebraska Act. Its anti-slavery stance was attractive to Seward, but he needed the Whig structure in New York to get re-elected. In September 1855, the New York Whig and Republican parties held simultaneous conventions that quickly merged into one. Seward was the most prominent figure to join the new party, and was spoken of as a possible presidential candidate in 1856. Weed, however, did not feel that the new party was strong enough on a national level to secure the presidency, and advised Seward to wait until 1860. When Seward's name was mentioned at the 1856 Republican National Convention, a huge ovation broke out. In the 1856 presidential election, the Democratic candidate, former Pennsylvania senator James Buchanan, defeated the Republican, former California senator John C. Frémont, and the Know Nothing candidate, former president Fillmore.
United States
The United States has operated under a two-party system for most of its history. For elective offices at most levels, state-administered primary elections choose the major party nominees for subsequent general elections. Since the general election of 1856, the major parties have been the Democratic Party, founded in 1824, and the Republican Party, founded in 1854. Since the Civil War, only one third-party presidential candidate—former president Theodore Roosevelt, running as a Progressive in 1912—has won as much as 20% of the popular vote. The President and Vice-president are elected through the Electoral College system.