At the start of the War of Independence, José María Morelos was instructed by Miguel Hidalgo y Costilla to spread the rebellion throughout southern Mexico, with his most important mission being the capture of Acapulco and the Fort of San Diego.

In February 1813, Morelos set out from Oaxaca with his army toward Acapulco, where insurgent Julián Ávila had already been threatening the area from the nearby Veladero hill. Morelos headed to the Costa Chica region with light artillery and a well-chosen force. The assault on the port and its fortress was a critical move for the independence cause.

For several months, insurgents and royalists engaged in fierce artillery battles, and the siege became a source of great suffering—marked by heat, hunger, and disease. On August 19, 1813, after six months of combat, the Spanish forces surrendered, and Captain Pedro Antonio Vélez raised the white flag over the fort. Thus, Morelos fulfilled the mission entrusted to him by Hidalgo.