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.
Republican Party (United States)
In the period 1850-1870, the Republican Party was more opposed to immigration than Democrats, in part because the Republican Party relied on the support of anti-Catholic and anti-immigrant parties, such as the Know-Nothings, at the time. In the decades following the Civil War, the Republican Party grew more supportive of immigration, as it represented manufacturers in the Northeast (who wanted additional labor) whereas the Democratic Party came to be seen as the party of labor (which wanted fewer laborers to compete with). Starting in the 1970s, the parties switched places again, as the Democrats grew more supportive of immigration than Republicans.