While opposition to slavery gained most of its momentum in the 19th century, its roots began much earlier. Some opposition to slavery was religiously based: The Quakers led the way in asserting opposition to enslavement for religious reasons. They staunchly argued against the immorality of its practice. Because of their tenets of the equality of all people and opposition to war and violence, Quakers successfully banned slavery in Pennsylvania in 1780; they were among the first to petition the US government to abolish slavery in 1790. As the 1800s began, more Northern states followed suit.

Abolitionists came from a variety of demographics, consisting of both white men and women as well as formerly enslaved Black people. Notably, there were differing opinions about how abolition should occur. For instance, in 1816, an organization called the American Colonization Society established a colony in land secured in western Africa for the rehoming of American enslaved people. For the next three decades, those freed from slavery were sent in groups—they were often families—to the small area of land that would later become Libya. Other abolitionists ranged from asserting all enslaved people should be given immediate and total freedom to arguing for gradual freedom, which could include a period of indenture-hood or freedom granted when an enslaved person reached a specific age.