Slavery, race, and abolition.  Before 1780 all the U.S. was a slave country or states.  It was in the Revolution that North became distinguished from South according to freedom and slavery.  This, the biggest distinction and division in American history--free states, slave states.

Forty percent of the population of the southern states consisted of black slaves.  They stood divided from the majority of the population by color, and their public and legal status (slavery and governed by slave law or codes).  Neither liberalism, nor republicanism, nor the Revolution was to apply to them, or make them one of the national body politic.  

Racially, men like Jefferson (above all others) who always maintained that they should be free, nevertheless believed they were divided from white people by creation (polygenesis), a different species (versus one species/monogenesis).  They were inferior and always would be.

At the constitutional convention of 1787, the issue of slavery arose repeatedly and ironically indicated a nation divided over the issue of slavery, but able to compromise on the issue. Compromise means coming together. In the convention there certainly was a compromise over the slave trade and one over the representation of slaves, the 3/5 clause.  See discussion of the Convention.