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.
History of the United States Republican Party
The Republican Party began as a coalition of anti-slavery Conscience Whigs such as Zachariah Chandler and Free Soil Democrats such as Salmon P. Chase, who were opposed to the Kansas–Nebraska Act, submitted to Congress by Stephen Douglas in January 1854. The Act opened Kansas Territory and Nebraska Territory to slavery and future admission as slave states, thus implicitly repealing the prohibition on slavery in territory north of 36° 30′ latitude, which had been part of the Missouri Compromise. This change was viewed by Free Soil and abolitionist Northerners as an aggressive, expansionist maneuver by the slave-owning South.