Mexico gained independence in 1821 following an armed conflict. The end of the war technically marks Mexican Independence but it was more complicated than that.

There were a tremendous number of factors leading to the decline of the Spanish Empire. The French briefly made a claim to Mexico in 1808. A host of historical processes were involved. Unfortunately, I am a bit tied up right now but will try to return to give you a more complete answer tomorrow.

For the meantime, a regime change from Hapsburg to Bourbon and the associated shift in policy (the Bourbon Reforms) contributed largely to the decline of the Spanish Empire. The reforms were meant to decrease corruption and modernize the empires administration, however this effectively changed the way business was done in the America’s since the arrival of the Spanish, and nobody liked it.

Across Spanish America, there was a well established Creole identity— meaning people of european decent born in the America’s. There had long been a sort of clashing between Creoles and Peninsular, often United only by their loyalty to the crown despite a difference of opinion on many aspects of colonial life/administration. This means wealthy upperclass and middle class people were more willing to support a split from Spain.

Indigenous and poor people had long struggled with colonial rule. Thought the history of the empire, revolts were prevalent, but not successful. Leading up to the fall of the empire things only heated up with rebellions that gained traction like that of Tupac Amaru II. Indiginous peoples and Casta people alike were willing to support a split to Spain.

The stage is set for Revolution.

Spain during all of this is greatly distracted by war with France in Europe. The war was an opportunity and led to revolts across the empire.

Back to Mexico, or as it was known at the time, the Viceroyalty of New Spain. The Bourbon reforms essentially curbed life as they knew it for the Creole elite. Years prior to the revolution there was a coup launched against a reformist viceroy. The coup was successful, but the multi-class revolt maintained that they were loyal to the crown and the viceroy was misrepresenting the crown (a similar thing happened in the US prior to the Declaration of Independence). The revolution however seems to be spontaneous and opportunistic.

Miguel Hidalgo, a small town priest wrote el “Grito de Delores” which sparked a revolt. Among the leaders was Allende, a famed military man. Battle ensued in cities around Queretaro like San Miguel de Allende, Atoetonilco (significant to the planning of the revolution), and Celaya. Spanish administrators were slaughtered. The viceroy raised a force to put down the rebellion, meanwhile the rebellion gathered support. Hildalgo. The revolt gathered a large following from Bajío and Jalisco and the violence continued. They were eventually chased north where some Spanish loyalists joined them under the pretense of joining the revolt. They were subsequently captured, tried, and executed. This essentially martyred them for the revolution. Dolores was renamed Dolores de Hildalgo, San Miguel renamed San Miguel de Allende. Namesakes of the original leaders are found all over Mexico and beyond.

The next 10 years (1810-1820) were marred by violent guerilla opposition to Spain, though it was still largely a peasant revolt. Then in 1820 when the revolt is all but put down, something changes in Spain— the Spanish monarch was ‘compelled’ to institute a liberal constitution which would make Spain a constitutional monarchy. The forces which were sent to put down the revolt actually did a complete 180 in light of the new constitution. After some negotiation they joined with the revolt. Less than a year later the Córdoba Treaty was signed under the Plan de Iguala.

Hope this helps, sorry it is so long. But there has to be a lot of background info to set the stage.