On 21 September 1792, the National Convention, the revolutionary assembly that had convened after the August insurrection, formally declared the end of the Bourbon monarchy and proclaimed France a republic. The decision followed months of political upheaval: the collapse of royal authority after the flight to Varennes (June 1791), the suspension of King Louis XVI by the Legislative Assembly in August 1792, and the invasion of the Tuileries on 10–11 August. The proclamation of the republic represented a fundamental constitutional and symbolic break with France’s ancien régime. The Convention met amid war and internal crisis. Revolutionary France was at war with several European powers, and the return of émigré nobles and counter-revolutionary uprisings created an atmosphere of emergency. Many delegates to the Convention were affiliated with factions such as the Girondins and the Montagnards; debates over the fate of the monarchy reflected differing political calculations and principles. The vote of 21 September annulled all royal authority, though the fate of the deposed king—Louis XVI—remained the subject of later legal proceedings and debate within the Convention. Abolishing the monarchy had immediate legal and administrative consequences. The Convention set about drafting new republican institutions, revising symbols of sovereignty, and redefining citizenship in republican terms. The declaration did not instantly resolve political divisions; the republic’s early years were marked by intense factional struggle, the Terror that followed in 1793–94, and continuing external conflict. Nonetheless, 21 September became a foundational date for republican government in France and was commemorated by later regimes and republican commemorations. Historians emphasize both the contingency and the deep roots of the move to republicanism. Some contemporaries and later scholars view the proclamation as the culmination of Enlightenment critiques of absolutism and of popular political mobilization that had been building since the 1780s. Others stress the role of wartime pressures, radicalization, and immediate security concerns in prompting delegates to sever the constitutional links to monarchy. The abolition of the monarchy in 1792 did not produce a stable, long-term government immediately. The Convention’s subsequent actions—trial and execution of Louis XVI in January 1793, the Reign of Terror under the Committee of Public Safety, and later thermidorian reaction—show the turbulent transition from a monarchy to a republic. Still, the formal end of the monarchy on 21 September remains a pivotal moment in French political history: it redefined sovereignty as residing in the nation (however variously interpreted) rather than in a hereditary king, and it set enduring precedents for modern republican governance in France and beyond. Where details are contested, it is important to note distinctions: some contemporaries dated the founding of the republic to the day the Convention proclaimed the abolition of the monarchy (21 September), while others later highlighted subsequent events—most notably the execution of Louis XVI—as more definitive breaks. The date nonetheless entered historical memory as the moment when the National Convention severed the legal existence of the monarchy and adopted republican forms and rhetoric.