The royalist factions in Buenos Aires had, by 1812, effectively been crushed, and a Creole front led by José de San Martín , the Sociedad Patriótica, sought full emancipation from foreign powers. However, unitarist and Federalist interests continued to battle for control of the capital, and struggles with pro-royalist forces continued to flare up across the old viceroyalty. The struggles after 1810 saw the emergence in the interior of Federalist caudillos , powerful local warlords with their own militias and even their own self-declared independent "little republics" or republiquetas . They recruited - or, rather, press ganged - their rank and file from among the slaves, indigenous peoples and gauchos of the countryside. The most famous caudillos were Artigas in the Banda Oriental, Estanislao López in Santa Fé and Francisco Ramírez in Entre Ríos.

While the war with Spain raged on, two congresses were convened to discuss the future of the former viceroyalty on a pan-regional basis, but these were dominated by unitarists and failed to produce a plan for the country on which all sides could agree. In the second, held on July 9, 1816 in the city of Tucumán, the independence of the United Provinces of the River Plate was formally declared, a title first adopted by Buenos Aires in 1813. It was largely ignored by the caudillos but the date, July 9, has since come to be recognized as Argentina's official independence day .

Later that year, San Martín led a disciplined force of five thousand men across the Andes to attack the Spanish in Chile, in one of the defining moments of Latin America's struggle against its colonial rulers. During this time, he was assisted in the north by another hero of Argentinian Independence, Martín Miguel de Güemes , an anti-royalist, Federalist caudillo whose gaucho army eventually liberated Salta. Though caudillos such as Güemes were in favour of independence, many resented the heavy taxes imposed to fund the struggles, and tensions remained high. Men like López and Ramírez defeated the attempt to impose a unitarist constitution in 1819.