Capitalism is, of course, a notoriously slippery term, fraught with ambiguities; its defenders, when they invoke it, tend not to mean what its detractors do, and both groups frequently and earnestly disagree amongst themselves. So while it may be that it is possible to reconcile slavery and capitalism, or even to say that the former is a central feature of the latter’s history, the free market that libertarians endorse must exclude slavery just by definition, slavery being the most extreme violation of the fundamental principles on which a genuine free market system is based.

Nineteenth century free‐​traders, forerunners of today’s libertarians, understood this well, even if the era’s capitalists (however indeed we define them) did not. It cannot be stressed enough that the period’s most outspoken and principled free‐​traders consciously and explicitly did not identify their free‐​trade philosophy with capitalism or with capitalists and their interests. Cobden decidedly did not see free trade as “a matter of advantage to the capitalists”—indeed the idea was “anathema to [him].” 5 Present‐​day arguments from left‐​wing scholars on the relationship between capitalism and slavery demonstrate a serious misunderstanding or outright ignorance of the basic fact that “the liberal principles of free trade” were frequently treated by free‐​trade advocates themselves as at odds with the interests of capital. It should not surprise us that some of the nineteenth century’s most articulate endorsements of free trade come from critics of capitalism like Thomas Hodgskin and Henry George. 6 American individualist anarchists like Lysander Spooner also number among those who saw the obvious philosophical connection between free trade and the abolition of slavery, emphatically favoring both libertarian causes. Spooner was an anti‐​capitalist who championed “free competition, and freedom from all arbitrary interference,” that is, radical laissez faire. Where today’s socialists reflexively bristle at the idea of international free trade, even many who counted themselves socialists in the nineteenth century joined with laissez‐​faire liberals, at least in principle, in regarding global free trade as the pathway from privilege, monopoly, and war to peace and prosperity. In his famous book Politics Among Nations, eminent scholar Hans J. Morgenthau, whose work pioneered political realism in the field of foreign policy and international relations, even grouped the libertarian socialist Proudhon with the liberal Cobden as among their generation’s 7 most principled “adherents of free trade.” Morgenthau argues that both Cobden and Proudhon “were convinced that the removal of trade barriers was the only condition for the establishment of permanent harmony among nations and might even lead to the disappearance of international politics altogether.” Today’s left doesn’t understand this part of its own history, and doesn’t care to.

As I’ve discussed in previous articles on this site, the political spectrum in use today simply does not give us language or concepts with which to make sense of thinkers like Hodgskin, George, Garrison, Spooner, Proudhon, and others. The notion that their libertarianism and support for free trade would put them on the political right is beyond absurd, underscoring the defects of the left‐​right spectrum more generally. As Matt Ridley writes, arguing for “free‐​market anticapitalism,” “Somewhere along the line, we have let the market, that most egalitarian, liberal, disruptive, distributed and co‐​operative of phenomena, become known as a reactionary thing.”