Theory’s Failure: Malthusian Population Theory and the Projected Demise of Slavery

During his debates with Abraham Lincoln in 1858, Stephen A. Douglas hit upon a weak spot in his opponent’s argument. In his “House Divided” speech, Lincoln had uttered the famous words: “Either the opponents of slavery will arrest the further spread of it, and place it where the public mind shall rest in the belief that it is in the course of ultimate extinction,” or it would grow and overwhelm republican institutions. Douglas, trying to tie Lincoln to abolitionism, asked how restricting slavery in the territories was going to produce emancipation in the slave states. He gave a partial answer: “When he thus gets it confined, and surrounded, so that it cannot spread, the natural laws of increase will go on until the negroes will be so plenty that they cannot live on the soil.” Thus the slaves will die by starvation and by that means “he will put slavery in the course of ultimate extinction.” “This is,” Douglas scoffed, “the humane and Christian remedy that he proposes for the great crime of slavery.”¹

Recent scholars have agreed that Douglas had a point and that instead of abandoning this line of thought in the next debate he should have continued to press Lincoln for an explanation.² How was slavery restriction going to produce emancipation? Douglas intimated the answer, in a crude way, that was widespread in the decades of the early republic: population pressure, an offshoot of Thomas Malthus’s theory of the effect of population growth on economic undertakings, was behind the public’s expectation that slavery if kept confined would eventually experience a natural death. But population theory, in either a general form or in a specifically Malthusian guise, generated considerable confusion among American leaders as to what effects population growth would have on the peculiar institution.³ The subject wove itself into considerations of agrarianism, wage rates, and emancipation, and it produced interesting conjectures from proslavery advocates, free traders, and protectionists–but not, intriguingly, from either British or American abolitionists.

When David Wilmot offered his proviso in 1846 to restrict slavery to its then existing boundaries, the debate over the impact of population growth upon the future of slavery took a decisive and ominous turn. Northerners often did not react like Lincoln in seeing a demise of slavery by some natural mechanism; instead, they pictured a more complicated scenario. Most important, southerners, though exhibiting some confusion in their predictions, believed that limiting slavery to its existing boundaries would produce poverty, depopulation of whites, and ultimately race war. In their search for an understanding of what the future might bring under the Wilmot prohibition, southerners were misled by classical economic theory; and thus they read into the Wilmot Proviso a more grim outcome than was likely. By this route, by leading southerners to miscalculate the effects of a prohibition against slavery’s geographical expansion, Malthusian population theory, and classical political economy in general, helped push the South to secession and the nation to civil war.

A widespread discussion of Malthusian population theory occurred in the early republic because, aside from the slavery question, it had implications for the stability of a republican form of government. Malthus’s theory was not difficult to grasp. The masses had bestial procreative instincts; they reproduced mindlessly at a faster rate than the growth of food production. Eventually, the population outstripped the food supply, and the only way equilibrium could be restored between the food supply and the number of people was to eliminate some people. At first, Malthus said this was done by wars, famines, and plagues; later he admitted that people might be trained to control their lusts and thereby halt the tendency to outstrip food supplies. The aspect of his theory that would play a prominent role in the sectional debate over slavery expansion was an economic argument about wages; wages for common people plunged to a subsistence (starvation) level because the supply of workers always exceeded the demand for them.⁴

In the United States after the Revolution, the two subjects of population growth...