The crisis began an ocean away. When Napoleon's armies invaded Spain and captured King Ferdinand VII, the Spanish empire in the Americas lost its center of gravity. In the Viceroyalty of the Río de la Plata, the capital city of Buenos Aires seized the moment: in the May Revolution of 1810 it ousted the viceroy and set up its own governing junta, the Primera Junta. Across the river, Montevideo refused to follow. It recognized the Cortes of Cádiz as Spain's legitimate authority and was rewarded by being named the viceroyalty's new capital, with its governor, Francisco Javier de Elío, promoted to viceroy. The Banda Oriental was now split against itself, town by town, between those loyal to Montevideo and those drawn to Buenos Aires.

Elío declared war on Buenos Aires on February 12, 1811, and to fund it he piled new taxes onto an economy already battered by the war in Spain. The burden pushed the rural population toward open revolt. Among the men changing sides was an officer who would become the most important figure in the region's history: José Gervasio Artigas, a respected leader of the eastern countryside who had served in the Spanish forces. On February 15, 1811, he abandoned the royalist garrison at Colonia del Sacramento and rode to Buenos Aires to ask for support for a rebellion of his own people. His defection lent the gathering insurgency both legitimacy and a leader.

The rising that Artigas helped set in motion was led on the ground by two local caudillos, Venancio Benavídez and Pedro Viera, acting on his instructions. Viera had begun rallying men in January with a band of just twenty-eight; by late February the movement had grown. On February 28, the assembled rebels at the Asencio stream pronounced against the authority of Elío, and the act rippled outward fast. The villages of San Carlos, Minas, Maldonado, Durazno, Canelones, and Pantanoso joined the pronouncement against Spanish rule. That same day the rebels took Mercedes in the morning and, under Viera, captured Santo Domingo de Soriano in the afternoon. Artigas himself joined the fight shortly after.

Historians count the Cry of Asencio as the start of the Oriental Revolution, the chain of events that would eventually carry the Banda Oriental out of Spanish control and toward independent statehood as Uruguay. What began with a hundred men on a stream bank grew within months into a popular army. That spring, the rebels pressed toward Montevideo itself, and on May 18, 1811, Artigas led them to a decisive victory at the Battle of Las Piedras, just north of the capital. The momentum he gathered at Asencio carried him into the first siege of Montevideo and into the role he is best remembered for, leader of a people in arms. The reverence Uruguayans hold for Artigas, the father of their nation, traces back in part to this earlier moment, when a Spanish officer chose his own people over his uniform. The Asencio stream still runs quietly through the cattle country of Soriano, but a country remembers that on its banks, ordinary rural people decided their future was theirs to claim. Each February 28, Uruguay marks the anniversary as one of the founding dates of its independence.