At first, African slaves made up a relatively small percentage of the population in the British colonies. Over time, the number of Africans and African Americans grew, and slaves came to occupy a distinctive class of their own, a class lying on the lowest rung on society's ladder. After the United States won its independence, the distinction between white laborers and black slaves hardened, as did the economic differences between the North and the South. A unique situation was developing in the New World, where the modern Industrial Revolution was developing hand in hand with one of the oldest and most backward institutions in human history.

In the home countries of Europe, where slavery was no longer practiced, the United States and slavery formed a popular topic of debate among social reformers, politicians, and journalists. The conditions of slavery also drew the strong interest of...