The Haitian Revolution and its aftershocks had a profound impact on American constitutionalism. The six administrations from George Washington through John Quincy Adams responded to the slave revolt and establishment of Haitian independence in ways that greatly expanded executive power and changed the nation’s approach towards the law of nations. The Executive took effective control over the nation’s most important dimensions of foreign policy, creating and employing instruments of power that are used to this day. For the first time, presidents unilaterally provided funds and military equipment to a foreign belligerent, intervened in a foreign civil war, negotiated secret commercial, diplomatic and military agreements with a foreign nation and the leader of a rebellion, used military force abroad, expanded the treaty and recognition powers and, with the acquiescence of the Supreme Court, violated accepted doctrines of the law of nations. These actions formed a blueprint for executive dominance over foreign policy, war and international law. This forgotten history is essential for a contemporary understanding of the foundations of modern presidential power over foreign affairs and war. Many of the most controversial questions presidents face in the modern era — whether to support regime change, use military force to protect American interests abroad, intervene in civil wars, arm foreign rebellions, form secret agreements with governments or belligerents, adhere to the requirements of international law — were first faced in the American reactions to the Haitian Revolution. Those decisions set precedents for the expansion of executive power whose legacies still exert a deep if unrecognized influence today. This article also illuminates the relationship of slavery to American foreign policy in the early Republic. The near-universal abhorrence and fear of a slave revolt was a powerful force in executive foreign policy decisions. But two other factors also influenced presidents in dealing with the Haitian Revolution — trade and geopolitics. When these other forces overcame domestic pro-slavery demands, presidents supported blacks fighting for their freedom and helped to create independence from the crucible of a slave revolt. However, when these forces were aligned with, or at least did not conflict with, the existential threat of a permanently successful slave revolt, the determination to isolate or crush the Haitian Revolution prevailed. As Haiti lost its strategic and economic importance to the United States, a consensus developed in the executive, legislative and judicial branches that, in the legal contemplation of the American government, the nation of Haiti did not exist.