Answer: In the 1850s, the issue of slavery—and its extension into new territories and states joining the Union—ripped apart these political coalitions. During this volatile period, new political parties briefly surfaced, including the Free Soil and the American (Know-Nothing) parties.
In 1854, opposition to the Kansas-Nebraska Act, which would permit slavery in new U.S. territories by popular referendum, drove an antislavery coalition of Whigs, Free-Soilers, Americans and disgruntled Democrats to found the new Republican Party, which held its first meeting in Ripon, Wisconsin that May. Two months later, a larger group met in Jackson, Michigan, to choose the party’s first candidates for statewide office.
The Republican goal was not to abolish slavery in the South right away, but rather to prevent its westward expansion, which they feared would lead to the domination of slaveholding interests in national politics.
In the 1860 election, a split between Southern and Northern Democrats over slavery propelled the Republican candidate Abraham Lincoln to victory, though he won only around 40 percent of the popular vote.
Even before Lincoln could be inaugurated, seven Southern states seceded from the Union, beginning the process that would lead to the Civil War.