To provide cojntext on my background knowledge i am a british student wiha base understanding of major events but I lack knowledge on the political realities and the personalities active at the time.
The Republican Party was still rather new in 1860. They were united on three main issues: High tariffs, free soil to farmers that wanted to develop farms in the Western territories and a Trans Continental Railroad. This allowed the Republican Party to pretty much absorb the Free Soil Party, which had been a strong third Party in the 1844 to 1852 time period. The Republicans were also a happy home for the anti-slavery wing of the Whig Party, which tore itself apart over the issue of slavery during the 1850s.