Father Miguel Hidalgo had launched the Mexican War of Independence just months earlier, in September 1810, rallying tens of thousands with his famous Grito de Dolores. By October, his insurgent army had marched toward Mexico City, but at the capital's gates Hidalgo made the fateful decision to turn back. His forces retreated toward Guanajuato, pursued by Calleja's disciplined Royalist troops. At Aculco, Calleja intercepted the insurgents and scattered them. Hidalgo pressed on toward Guadalajara, where he regrouped and swelled his ranks to an enormous force. But size is not discipline. Among those 100,000 followers, only 20,000 were light cavalry, and just 3,000 carried muskets. The remaining 60,000 were armed with spears, slings, and arrows against professional soldiers equipped with artillery and modern firearms.

Ignacio Allende commanded the insurgent position at the bridge, a natural chokepoint where terrain should have favored the defenders. Calleja's smaller force arrived on January 16 and engaged the next day. The battle that followed was not decided by strategy or valor but by catastrophic luck. Royalist artillery struck an insurgent ammunition wagon, and the resulting explosion sent a shockwave of panic through the loosely organized rebel ranks. Soldiers armed with spears and slings, already outmatched in firepower, broke and fled. The disciplined Royalist troops pressed their advantage as the insurgent force disintegrated. What had been the largest army in the independence movement scattered northward in chaos, with Royalist troops in pursuit. The battle marked the end of the war's first phase and proved that passion alone could not defeat professional military power.

The aftermath was swift and merciless. In Pabellón de Hidalgo, the surviving insurgent leaders stripped Hidalgo of military command, transferring authority to Allende. The group fled northward, hoping to reach the United States to purchase weapons. In March 1811, General Ignacio Elizondo of Nuevo León invited them to meet at the Wells of Baján in Coahuila, promising safe passage. It was a trap. Allende, Juan Aldama, Mariano Jiménez, and Allende's son Indalecio arrived first and were immediately seized. When Mariano Abasolo arrived with a second group, they too were captured. Hidalgo rode in last, on horseback, and Elizondo personally apprehended him. The leaders who had mobilized a nation were now prisoners, delivered by one of their own.

The captured leaders were taken to Chihuahua for trial. Allende, Aldama, and Jiménez were executed by firing squad on June 26, 1811. Hidalgo, the priest who had started it all, was shot on July 30. Abasolo received a sentence of life imprisonment in Cádiz, Spain, where he died in 1816. Their deaths did not end the independence movement, but the loss at Calderón Bridge and the execution of its leaders scattered the rebellion into guerrilla resistance that would grind on for another decade. Mexico would not achieve independence until 1821. The Spanish commander Calleja was rewarded with the title Conde de Calderón for his victory, and eventually became Viceroy of New Spain. In 1932, the site of the bridge was declared a Mexican historical monument, a quiet place along the river where the course of a nation pivoted on a single, unlucky explosion.