Which political party was founded in the 1850s to oppose the expansion of slavery?

The Republican Party was founded in the 1850s with a primary goal of opposing the expansion of slavery into the territories of the United States. This emergence was a direct response to the controversial Kansas-Nebraska Act of 1854, which allowed for the possibility of slavery expanding into new territories based on popular sovereignty, igniting significant national debate and conflict. The Republican Party attracted a coalition of former Whigs, Free Soilers, anti-slavery Democrats, and abolitionists who were united in their opposition to the spread of slavery. This platform would later contribute to the party's rise in prominence and its role in the election of Abraham Lincoln as the first Republican president in 1860, a pivotal moment in American history that led to the Civil War and significant changes in the nation's approach to slavery.

The other parties mentioned either had different focuses or were established prior to the intensifying debates over slavery. The Democratic Party, for instance, had factions that supported slavery, particularly in the South. The Whig Party was fracturing during this time, with many of its members ultimately joining the Republicans. The Federalist Party was already defunct by the 1850s, having lost influence in the early 19th century. Thus, the context