The battles, political and physical, over slavery are also demonstrations of constitutional patriotism in the United States, as they demonstrate the alteration of norms and values. In the mid 1780s. hundreds of thousands of slaves served as the cornerstone of American production. The constitution's defense of the rights of slave owners created a rift in the values of America:half of the country adhered to the Declaration of Independence's belief that 'all men are created equal' while the other half adhered to the constitution's ruling which allowed slavery. The rhetoric of many anti-slavery protesters appealed to the Constitution and Declaration of Independence in order to resolve this split in interpretation. Frederick Douglass stated that "the Constitution of the United States, standing alone, and construed only in the light of its letter, without reference to the opinions of the men who framed and adopted it, or to the uniform, universal and undeviating practice of the nation under it, from the time of its adoption until now, is not a pro-slavery instrument." Similar rhetoric led to the 13th Amendment to the United States Constitution and a universal anti-slavery constitutional patriotic view, changing the norms and values of society, which were then reified in the Constitution.