A History of the Slave-Breeding Industry in the United States

By a conservative estimate, in 1860 the total value of American slaves was $4 billion, far more than the gold and silver then circulating nationally ($228.3 million, “most of it in the North,” the authors add), total currency ($435.4 million), and even the value of the South’s total farmland ($1.92 billion). Slaves were, to slavers, worth more than everything else they could imagine combined.
— Read on kottke.org/16/02/a-history-of-the-slave-breeding-industry-in-the-united-states