The Federal League (Spanish: Liga Federal), also known as the League of the Free Peoples (Liga de los Pueblos Libres), was an alliance of provinces in what is now Uruguay, Argentina and Brazil that aimed to establish a confederal organization for the state that was emerging from the May Revolution in the war of independence against the Spanish Empire.

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 delegates from these provinces were rejected on formalities from the Congress that declared the independence of the United Provinces of South America on July 9, 1816.

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. In 1820, the federalist governors of Santa Fe and Entre Ríos provinces, Estanislao López and Francisco Ramírez, defeated a diminished Directorial army, ending the centralized government of the United Provinces and establishing a federal agreement with Buenos Aires Province.

The league was dissolved after its constituent provinces rejoined the United Provinces, now under a federal provisional organisation, and after the invasion of the Banda Oriental by the United Kingdom of Portugal, Brazil and the Algarves and the defeat of Artigas. 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. It was instrumental in the Guaraní participation in the revolutionary cause.

Although the country was intended to extend throughout modern-day Argentina, its leadership was based on Purificación and the Eastern Bank of the Uruguay River. Therefore, it is sometimes considered a predecessor state of modern Uruguay.

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 situation was clear: with the authority of the vice-regency gone, there was a power vacuum. Leading figures in Buenos Aires quickly arranged a meeting and after much discussion it was decided to replace the Spanish rule with a local Junta.

After the May Revolution, most of the provinces of the former Viceroyalty of the Río de la Plata joined to form the United Provinces of the Río de la Plata, also known as United Provinces of South America in 1810. The four provinces of Upper Peru (current-day Bolivia) were occupied by Spanish Royalist forces and the other ten provinces were under pressure from Royalist forces.

In 1810, Spain moved the headquarters for the Viceroyalty of the River Plate to Montevideo after the May Revolution forced them to abandon Buenos Aires. On February 15, 1811 José Gervasio Artigas left his home of Montevideo and moved to Buenos Aires to offer his military services. The people of Spanish America were fighting for their freedom and Artigas wished to defend these ideals in the Eastern Bank. At the beginning of April he returned to his country with approximately 180 men provided by the Government of Buenos Aires; on April 11, he issued the Mercedes Proclamation, assumed control of the revolution and on May 18 defeated the Spanish in the Battle of Las Piedras. He then began the siege of Montevideo and was acclaimed as The First Chief of the "Orientals" (the first names of current Uruguay being Banda Oriental (Eastern Bank) and later Provincia Oriental (Eastern Province), Uruguayans thus refer to themselves as 'Orientales').