Mexican War of Independence
Although Mexico gained its independence in September 1821, the marking of this historical event did not take hold immediately. The choice of date to celebrate was problematic, because Iturbide, who achieved independence from Spain, was rapidly created Emperor of Mexico. His short-lived reign from 1821–22 ended when he was forced by the military to abdicate. This was a rocky start for the new nation, which made celebrating independence on the anniversary of Iturbide's Army of the Three Guarantees marching into Mexico City in triumph a less than perfect day for those who had opposed him. Celebrations of independence during his reign were marked on September 27. Following his ouster, there were calls to commemorate Mexican independence along the lines that the United States celebrated in grand style its Independence Day on July 4. The creation of a committee of powerful men to mark independence celebrations, the "Junta Patriótica", organized celebrations of both September 16, to commemorate Hidalgo's grito and the start of the independence insurgency, and September 27, to celebrate actual political independence.
First Mexican Republic
The Spanish overseas possession of the Viceroyalty of New Spain lasted for 300 years, from 1521 with the fall of the Aztec capital of Tenochtitlan and the foundation of Mexico City until the collapse of the viceroyalty in following years of civil war and military stalemate. An insurgency for independence from Spain lasted from the initial 1810 mass revolt, led by secular cleric Miguel Hidalgo and continued under another secular cleric, José María Morelos, and carried on the hot country of Mexico's south by Vicente Guerrero. Augustin Iturbide, a royalist military officer born in New Spain of Spanish parents, made a strategic alliance with Guerrero under the Plan of Iguala, in which the former foes fought in tandem to oust Spanish rule. The plan proclaimed Mexico a nation-state; Roman Catholicism as the sole religion; the equality of Spaniards and American-born Spaniards and abolished legal racial designations, and was to be a constitutional monarchy. On September 27, 1821, Mexico obtained its sovereignty under the Treaty of Córdoba, which recognized New Spain as an independent empire, which took the name the Mexican Empire.