Look up the Articles of Confederation. That was the country's weak, ineffective governing document before the Constitution. Then look up the 1787 Constitutional Convention. You'll see that slavery at that time had not yet caught fire as the hugely divisive issue it would become by the mid-1800s. Back around the time of the Constitutional Convention, the big issue for U.S. Leaders was how to make the country a truly strong, unified nation, not just a weak association of independent states. They wanted to create a national government that was powerful enough to be effective, but they also wanted to make sure that there were limits on the government's power so that people's liberty would be protected.