The issue of slavery was a major underlying issue to the formation of the Republican party.
On May 20th, 1854, a group of politically- minded former Whigs met in Ripon , Wisconsin to talk about the possibility of forming a new political party that would focus on preventing the spread of slavery in the Western territories. The idea took off and on June 6th 1854, over 10,000 people gathered in Jackson, Michigan to establish the new party and thus the Republican party was born.