Inspired and led by José Gervasio Artigas, it proclaimed independence from the Spanish Crown in 1815 and sent provincial delegates to the Congress of Tucumán with instructions regarding the nonnegotiable objective of declaring full independence for the United Provinces of the Río de la Plata and establishing a confederation of provinces, all of them on equal footing and the government of each being directly accountable to its peoples by direct democratic means of government.

The Federal League confronted the centralist governments, as well as the interests of the economic and cultural elite of Buenos Aires and Montevideo, in what later amounted to a civil war.

At its largest extent, the League extended over the territories of present-day Uruguay, the southern Brazilian state of Rio Grande do Sul and the Argentine provinces of Entre Ríos, Santa Fe, Corrientes, Misiones and Córdoba.

On May 13, 1810, the arrival of a British frigate in Montevideo confirmed the rumors circulating in Buenos Aires: France, led by Emperor Napoleon, had invaded Spain, capturing and overthrowing Ferdinand VII Bourbon, the Spanish King.

The Portuguese forces, led by Carlos Frederico Lecor, thanks to his numerical and material superiority, conquered the Eastern Province and took Montevideo on January 20, 1817, but the struggle continued for three long years in the countryside.

Infuriated by Buenos Aires's passivity, Artigas declared war on the Supreme Directorship at the same time that he faced the Portuguese with armies that were being decimated by successive defeats.