In 1828, the Democratic Party was founded by President Andrew Jackson, a general and a slave owner. The party was founded on the Jacksonian promise that Americans, or in this day at that time, White Americans, will dominate the North American continent out of a belief that White America is divinely entitled by the ordination from God as the "superior race", referring to a Democratic Party-orchestrated plan called "Manifest Destiny". This plan included the ethnic cleansing and relocation of Native Americans, expanding the border of the United States to strengthen the power of Slavery over African-Americans, and forced Cultural Assimilation.
The Democratic Party's support for Slavery began to collapse on them in the elections of 1860, free white laborers feared the expansion of slavery and refusing to compete with the slave labor taking place mostly in the Southern United States, but the Southern States resisted a Lincoln Presidency, the Southern Economy relied heavily on agriculture, while the North was heavily industrialized, African-American slaves were the dependable resource that keeps American agriculture alive at the time, putting the South in deep fear that the newly elected President Lincoln will take away slavery despite Lincoln promising he would have no such thing, this Southern paranoia forced them to rebel against the United States, form their own nation, and start the most bloodiest war in American History, known as the American Civil War, or as the South calls it in a fancy way "The War of Northern Aggression" The war was so bad that the desperate Lincoln and his Republican Party controlled Government was forced to accept the reality that permanently emancipating black people from slavery via Constitutional Amendment will solve this national problem and freeze the possibility of another civil war over this subject. That's when the 13th Amendment comes in.