Much of the impact was psychological rather than material. In other words, there was no Haitian army of liberation landing on the shores of South Carolina to overthrow the Slave Power. But it scared slaveowners in the United States. A lot.
It's important to keep in mind is that slaveowners suffered from political paranoia, which they spread as widely as possible among nonslaveowning whites, as well. William Freehling talks about the "Cuffee" phenomenon. By which he means that slaveowners were aware at some level that the agreeable face their slaves were expected to present to them was a false one. And they constantly worried that there were hidden threats in everyday interactions with their human property. It created a state of mind that predisposed them to panic over alleged slave revolts. And indeed, there were many more slave panics over slave revolts than there were of the real thing.
But there were real slave revolts. The study of slave resistance has revealed a very complex set of resistance actions and strategies. The Underground Railroad, for instance, was a critical one. Not every one of them involved some kind of uprising. But there were some of those, too.
And the Haitian revolution was a big-time instance of one. Horne call it:
... one of those rare transformative social, political, and economic detonations made all the more remarkable in that it took place in not only the richest and most productive colony of the French Empire, but of any empire. But it also implicated the slaveholding republic in that Paris spent heavily in backing North American rebels opposing their eternal enemy across the channel, which contributed to a crisis in Paris that sparked yet another transforming revolt in 1789, which correspondingly contributed mightily to the radicalization of the island. Correspondingly, revolutionary violence in France and Hispaniola seemed to some U.S. citizens to flow together in a common river of blood that signaled a new departure that could reach the mainland. This was ironic indeed since North American-then U.S.- residents were heavily implicated in the dramatic increase of the slave trade to the island of Hispaniola, which in the 1780s surpassed the British trade, creating a demographic imbalance favorable to a slave revolt. [my emphasis]Yes, Haiti was "the richest and most productive colony of the French Empire." And the successful slave revolt there scared white slaveowners in the United STates. A lot.
Horne goes further and argues that "the Haitian Revolution created a general crisis for the system of slavery that could only be resolved with its collapse." He even calls it "a central argument of this essay."
That seems a bit of a stretch to me. But there were important international dynamics at work that I'm hesitant to dismiss. Horne cites these events:
But it was in 1795 in Spanish Louisiana - apparently encouraged by the possibility of a French attempt to invade and force retrocession of the former colony - that Africans rose up. This slave conspiracy in Pointe Coupee was blamed by those on the scene on the direct influence of island revolutionaries. There had been an extensive plot in July 1791, days before the ignition in Hispaniola, then again in October when one conspirator was said to have stated that he and his comrades were simply awaiting ward from Hispaniola before deciding to "strike a blow" in concert with islanders. After the uproar of 1795 there were additional slave conspiracies in February, March, and April 1796 in Pointe Coupee and on the German Coast.Proslavery whites who had emigrated from Haiti brought some of their fear of slave revolts with them:
A contemporary historian has estimated that "over 100,000 whites and 60,000 blacks lost their lives" during the "thirteen year struggle" encapsulated as the Haitian Revolution, 1791-1804. That more defined as "white" perished, though their numbers were considerably smaller than their counterparts-less than 500,000 Africans on the island then- with many survivors fleeing to the mainland imbued with hair-raising tales of woe, was bound to concentrate devilishly in the collective mind of "white" Americans. The revolution posed starkly an existential choice: retreat stolidly from slavery or risk losing everything, including one's life, a la Hispaniola. ...As Horne summarizes it, "These newly minted "white Americans" were hardly in the mood to retreat in the face of African demands, particularly those backed by Haiti (and London)."
That so many of these survivors and their relatives wound up playing pivotal roles in maintaining the harshest machinery of slavery on the mainland may not have been accidental. This lengthy list included Judah P. Benjamin, a loyal leader of the Confederate States of America, whose father-in-law fled the island in horror and proceeded to regale many an audience with the alleged perfidy of incited Africans. Louis Tousard, who served in the revolt against British rule in North America, also owned a plantation on the rebellious island, an enterprise that was marred by frequent unrest in the 1780s. He was involved in seeking to suppress the revolt in 1791 before fleeing to the mainland where, tellingly, he was intimately involved in establishing the U.S. Military Academy at West Point, New York, which was to be both the sturdy sword and shield, if plans by vengeful Africans to invade the mainland and ignite the vengeance of the enslaved were to come to pass.
Horne notes that "the horrors of St. Domingo" became "a catchphrase summarizing the knife's edge on which slavery rested."