In 1813, the new government in Buenos Aires convened a constituent assembly where Artigas emerged as a champion of federalism, demanding political and economic autonomy for each area, and for the Banda Oriental in particular. The assembly refused to seat the delegates from the Banda Oriental, however, and Buenos Aires pursued a system based on unitary centralism.
As a result, Artigas broke with Buenos Aires and besieged Montevideo, taking the city in early 1815. Once the troops from Buenos Aires had withdrawn, the Banda Oriental appointed its first autonomous government. Artigas organized the Federal League under his protection, consisting of six provinces, four of which later became part of Argentina.
At the time of independence, Uruguay had an estimated population of just under 75,000. The era from independence until 1904 was marked by regular military conflicts and civil wars between the Blanco and Colorado Parties. The political scene in Uruguay became split between two parties: the conservative Blancos (Whites) headed by the second President Manuel Oribe, representing the agricultural interests of the countryside; and the liberal Colorados (Reds) led by the first President Fructuoso Rivera, representing the business interests of Montevideo. The Uruguayan parties received support from warring political factions in neighboring Argentina, which became involved in Uruguayan affairs.
The Colorados favored the exiled Argentine liberal Unitarios, many of whom had taken refuge in Montevideo while the Blanco president Manuel Oribe was a close friend of the Argentine ruler Manuel de Rosas. On 15 June 1838, an army led by the Colorado leader Rivera overthrew President Oribe, who fled to Argentina. Rivera declared war on Rosas in 1839. The conflict would last 13 years and become known as the Guerra Grande (the Great War).