When the United States' Constitution was being written, one of the issues being debated was how representatives should be allocated to each state. Though the delegates agreed that one house of Congress, the House of Representatives, would be based on population, how population was totaled for determining the representation within that house was strongly debated. At the time, slavery was still legal in the country. The dilemma the delegates faced was how to count slaves for the purposes of representation.
Free States Proposal
The states that did not have slaves thought that it would be unfair to count slaves for the purposes of representation because it would give an unfair advantage in representation to the Southern states. The antislavery states were located in the northern half of the country and included Pennsylvania, Massachusetts and New York.
The states that allowed slavery were located in the southern half of the country and included Virginia, the Carolinas and Georgia. These states feared that if slaves were not counted as people for representation, the Northern states would have a significant advantage in representation and could use that advantage to limit or even abolish slavery.
The delegates reached an agreement that slaves would count as three-fifths of a person for the purposes of determining representation. For example, 100 slaves would be equivalent to 60 people. Because the delegates did not want to use the word "slave" in the document, they stated that "free persons" would count as one and "non-free persons" would count as three-fifths of a person.
Regulation of Slavery
The delegates also debated over what power the new national government would have to regulate slavery and the slave trade. Southern states were afraid that Northern states would push through legislation limiting the importation of slaves and possibly even outlawing slavery. As a compromise, the delegates agreed that the new government could not outlaw the importation of slaves until at least 20 years after the institution of the new constitution.
The three-fifths compromise remained in effect until the end of the Civil War. After the conclusion of the war, the 13th Amendment was passed that made all former slaves citizens, and therefore they were counted as full citizens for the purpose of representation.