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.
Treaty of Córdoba
On September 27, 1821, the Army of the Three Guarantees entered triumphantly into Mexico City and on the following day, the Declaration of Independence of the Mexican Empire was widely known. The Spanish Cortes refused to accept the validity of the Plan of Iguala or the Treaty of Córdoba. Spain did not recognize Mexico's independence until December 1836. Therefore, the Mexican Congress elected a Mexican monarch the following year. Iturbide was proclaimed emperor of Mexico on May 18, 1822. The monarchy lasted three years, and after the republican revolution of Casa Mata, the Congress no longer considered the Plan of Iguala or Treaty of Córdoba in effect.