Decree from Agustin Iturbide urging adoption of the Plan de Iguala

Army general Augustin de Iturbide (1783‒1824) galvanized Mexican support for independence. After a decade of fighting, Iturbide negotiated the Plan de Iguala, which set the terms under which Mexico defined its identity as an independent nation.

On September 16, 1810, Roman Catholic priest Miguel Hidalgo y Costilla (1753–1811) initiated the Mexican War of Independence with a call for armed revolt against ruling Spanish authorities. The start of the War is rooted in turmoil in Europe after Spain was invaded and occupied by French forces during the Napoleonic Wars. The conflict and political upheaval in Spain galvanized the people living in its American colonies to determine their own future. American-born Spaniards initiated an insurgency against colonial powers but in the decade of fighting afterward, Indigenous and mixed race people, hoping for an end to the Spanish casta system, became key players in the Mexican War of Independence.

Hidalgo's Grito de Dolores inspired thousands to fight. Despite not being a disciplined army, the size and intensity of their uprising was a shock to royalist Spanish leaders. Hidalgo's execution in 1811 gave way to other leaders who joined and continued the fight over the next ten years. Over the course of the War, battles took place all over New Spain, even reaching as far north as what is now Texas. In 1813, the Battle of Medina saw Spanish forces defeat revolutionaries in the deadliest battle in Texas history. To the south, leaders like José María Morelos (1765‒1815) and Vicente Guerrero (1782‒1831) built a more organized and disciplined army and successfully used guerilla tactics to defeat the Spanish in several battles between 1811 and 1820.

Army general Augustin de Iturbide (1783‒1824) got rival rebel leaders to accept an alliance and in 1821, announced the Plan de Iguala, which contained their shared goals. The Plan declared Mexico as an independent nation, established its official religion as Catholicism, and abolished the Spanish caste system by recognizing all residents as citizens. As citizens, people would have equal rights regardless of their race and place of birth. The document called for the newly unified forces, the Army of Three Guarantees, to protect religion, independence, and union. Most of the country rallied behind the Plan and shortly afterwards, Spanish authorities agreed to end the fighting. On August 24, 1821, Iturbide and Spanish authorities signed the Treaty of Córdoba which formally established Mexican Independence from Spain.