An American paradox

In 1775, after a decade of colonial protest over parliamentary taxation, Samuel Johnson famously complained, “How is it that we hear the loudest yelps for liberty among the drivers of negroes?” It was a good question and one that has dogged Americans ever since. That strident demands for freedom and equal rights under law came from a place where slavery was interwoven with everyday life, both North and South, has been called the central paradox of American history. As the dean of American historians, Edmund S. Morgan, wrote in the introduction to his own effort to unravel the problem, American Slavery, American Freedom (1975), “The paradox is American, and it behooves Americans to understand it if they would understand themselves.”

That chattel slavery contributed to the formation of the world’s longest-lasting republic is both true and almost beyond modern comprehension. In 1790, the nation’s...