Slaves were seen as lesser people in the populous, in terms of representation, slave numbers were considered 3/5 of what they were, and the issue of slavery was not pushed in the two key debates in fear that it would lead to the Southern states distancing themselves.
A common element in the two key debates at the Convention regarding representation in Congress and slavery was the amount of people involved.
Explanation:
Once the delegates of the Constitutional Congress agreed on having two chambers: The House of Representatives (which would be based on the number of population), and the Senate (which would be based on equal representation for each state, regardless of the number of population), they had another isse: how slaves would be counted. The North feared that the South would gain more representatives as the number of slaves was greater there. So, they proposed the Three-Fifths Compromise, which would count three individuals out of five slaves. Also, the slave trade would continue (people from the North wanted to end slavery but they were strongly opposed by the southerners and could not reach an agreement)