During the build up of the new constitution, the North and the South debated whether slaves should be counted in the population. If they did, they would count for the amount of representatives in congress.
We must decide if slaves should count for Representation.
Well, what do you think, the North states?
In the South, almost half of the population were slaves. Because higher population resulted in more representatives in Congress, the South argued that slaves should count for the amount of population in each state.
The Slaves should be counted as population, to help our representatives!
But the North didn't hold many slaves, and argued that slaves were treated as "cattle" and should be taxed like other people if they counted as the population.
Slaves are not valued as people, and are owned!
Many owners wanted to free their slaves after the American Revolution and other factors, and found this as a chance to do so. Laws were put in place to make it easy to free a slave.
I don't need you anymore. Leave.
But even still, the North and the South had been bitterly debating about this controversy. The South knew that if they won, slaves would contribute to the population, but if the North won, they would not.
Finally, after a long time of debating, James Madison came to the conclusion that slaves would be worth 3/5 of a person. They would still count for population and representation.