Army of the Three Guarantees
After switching sides, Iturbide chose to pressure the colonial government by repeating Hidalgo's strategy of closing in on the city from the surrounding area. Iturbide was able to succeed where Hidalgo had not because the Spanish-born commanders in the city supported Iturbide's idea of limited autonomy, and many the royalist forces were in the field battling insurgents like Guerrero. Iturbide's Army of the Three Guarantees (Independence, Union, Religion) entered Mexico City on 21 September 1821. On the following 27 September, Mexico was declared independent.