jats:pThe British–Irish Union of 1801 remains a significant and controversial moment in the histories of both countries, but understandings of its genesis are restricted inscope. This article seeks to place the Union in a new historical context: the crisis of the European states system that accompanied the French Revolution. It considers the position held by the Union in the critique of Kant's famous essay on “Perpetual Peace” (1795) advanced by one of his most influential students, the publicist and state official Friedrich Gentz (1764–1832). Gentz argued that the consolidation of the British state offered a model for the regeneration of European society. Only unitary forms of sovereign authority could exercise the responsible political agency required for the restoration of peace in the wake of the Revolution. The decline of small states and composite polities supported the durable civil liberty and commercial development necessary to mankind's moral development in history.</jats:p>