Answer:
After the American Revolution, which had been based on the fundamental principles of the freedom and equality of men and which had embodied in its main documents (the Declaration of Independence and the Constitution) these rights as fundamental pillars of the organization of the United States as a nation, the north of the country (which was the cradle of the revolutionary movement) embraced abolitionist positions, with the objective of expanding the concept of freedom to all the inhabitants of the nation. Thus, in the north, the position of abolishing slavery and guaranteeing the rights of African-Americans began to be defended, based on the equality of men and their right to the same opportunities as whites.
This vision was not shared in the south of the country, where the economy was practically based on the agricultural exploitation carried out by slaves, with which slavery was necessary for the maintenance of this system.
Therefore, anti-slavery pressure from the north and the persistence of this system in the south led both societies to face each other politically, with the violence increasing progressively and constantly until the start of the Civil War in 1861.