Delegates from several provinces met in San Miguel de Tucumán to decide a long-term political plan for the former Viceroyalty of the Río de la Plata. The meeting was called in a moment of military pressure from Spanish royalist forces and growing disagreements among the provinces about how to govern.
The Congress formally declared independence from the Spanish monarchy. This shifted the struggle from autonomy claims to an open break with Spain, aiming to strengthen legitimacy at home and abroad while war continued.
After independence was declared, Juan Martín de Pueyrredón became Supreme Director, the leading executive authority of the United Provinces. His government focused on keeping the war effort going and trying to hold the provinces together under a central authority.
With independence declared, José de San Martín advanced the broader strategy of weakening Spain by attacking royalist power on the Pacific side. He began the campaign that crossed the Andes from the Cuyo region toward Chile, aiming to remove a major royalist threat to the west and open a route toward Peru.
The Congress moved its sessions to Buenos Aires, the main political and economic center. This relocation increased tensions with provinces that feared stronger central control and felt distant from decision-making.
San Martín’s Army of the Andes defeated Spanish royalist forces at Chacabuco, helping secure Santiago and pushing the royalists back. The victory made it harder for Spain to threaten the United Provinces from Chile and strengthened the independence cause in the region.
The combined patriot forces defeated the royalists at Maipú near Santiago, a decisive step in securing Chile’s independence. This reduced the immediate risk of a major royalist return through Chile and supported San Martín’s plan to take the fight to Spanish strongholds farther north.
The Congress framed and promulgated the Constitution of 1819, designed to create a strong national executive under a Supreme Director. Many provinces rejected it as overly centralist, escalating the conflict between “unitarian” centralizers and “federal” provincial leaders.
Opposition to the central government and the 1819 constitution intensified, weakening the Supreme Directorship. Pueyrredón resigned, and leadership passed to José Rondeau as conflict among provinces deepened.
Officers of the Army of the North revolted at Arequito, refusing to fight fellow provinces in an internal civil war. This reduced the central government’s ability to enforce the constitution and contributed to the breakdown of national authority just before major fighting.
Federal provincial forces defeated the central government’s army at Cepeda. The defeat effectively collapsed the Supreme Directorship and led to the abandonment of the 1819 constitutional project, marking a sharp turn toward provincial autonomy.
After Cepeda, the national Congress dissolved, removing the main institution that had declared independence and attempted to build a centralized state. The political vacuum helped trigger a period often described as the "Anarchy of 1820," with provinces acting more independently.
Buenos Aires, Santa Fe, and Entre Ríos signed the Treaty of Pilar to stop fighting and set a basis for reorganizing relations among provinces. The pact is often treated as an early foundation of Argentine federalism, even though broader national stability remained unresolved.
Congress of Tucumán, the Declaration of Independence and its immediate aftermath (1816–1820)