Frederick Douglass, a former slave, and prominent abolitionist used the founding principles of America to build an argument against slavery in several ways.
First, Douglass argued that slavery was fundamentally incompatible with the principles of equality and liberty that were central to the founding of the United States. He pointed out that the Declaration of Independence, which was adopted by the Continental Congress in 1776, declared that "all men are created equal" and that they are "endowed by their Creator with certain unalienable Rights," including the right to "Life, Liberty, and the pursuit of Happiness." Douglass argued that these principles applied to all people, regardless of race, and that slavery, which treated people as property and denied them basic rights and freedoms, was a gross violation of these principles. Second, Douglass appealed to the ideals of democracy and self-governance that were central to the American Revolution. He argued that slavery was fundamentally undemocratic, as it gave slaveholders the power to control and exploit their slaves without any recourse or accountability. Douglass argued that in a true democracy, all people have a say in the decisions that affect their lives, and that slavery was fundamentally incompatible with this principle.
Overall, Douglass used the founding principles of America to build a powerful argument against slavery and to call for its abolition. His arguments were influential in the abolitionist movement and helped to build support for the end of slavery in the United States.