The writers of the Constitution thought that it was more important to form a nation than to end slavery.
They decided not to refer to slavery in the Constitution. This is why the original Constitution did not use the words “black,” “Negro,” ‘African;’ or “slave.” However, in three places in the original Constitution, it is clear that they are being referred to.
In Article I, section 2, the Constitution said that states would be taxed according to their populations plus “three-fifths of all other persons.” The phrase “all other persons” referred to blacks, and put that way meant that blacks were considered less than full human beings.
The second reference was in Article I, section 9, which stated that the “importation of certain persons” (the slave trade) could be stopped after 1808, and that Congress could then put a tax on anyone brought into the United States as a slave.
The third reference to slaves was in Article IV, section 2. It said that anyone escaping from bondage into another state would not be released from their labor, but would be returned to the party to whom they owe their service. This meant that runaway slaves would have to be returned to their masters.
These clauses in the Constitution recognized the existence and legality of slavery without actually saying so. They were later eliminated by constitutional amendments.