Alternative History
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War of the Río de la Plata

Rebellion of New Spain
Beginning:

16 September 1810

End:

15 November 1821

Place:

New Spain

Outcome:

Spanish victory

Major battles:

Battle of Monte de las Cruces

Battle of the Bridge of Calderón

Battle of Mexico

Battle of Durango

Combatants

Spanish Empire

British Empire (since 1819)

New Spain

Commanders

Ferdinand VII

Arthur Wellesley

Agustín de Iturbide (before 1820)

Miguel Hidalgo y Costilla

José María Morelos

Agustín de Iturbide (after 1820)

Strength
Casualties and Losses

(Note: The next paragraph was copied from Wikipedia, with small changes)

The Rebellion of New Spain (1810–1821) was an armed conflict between the people of New Spain and the Spanish colonial authorities which started on 16 September 1810. The Rebellion was led by New Spaniards, Mestizos and Amerindians who sought independence from Spain. The movement for independence was far from gaining unanimous support among New Spaniards, who became divided between independentists, autonomists and loyalists.

Miguel Hidalgo y Costilla declared war against the colonial government on the late night of 15 September 1810. After several victories, the rebels failed to defeat the large and heavily armed Spanish army in Mexico City. After retreating, the rebel forces fought the Battle of the Bridge of Calderón and lost, subsequently fleeing to the border of United States. The Spanish army, however, caught up with them and captured them. Hidalgo was executed on 30 July 1811.

However, this was not the last of the Rebellion. The leadership of the Rebellion was assumed by José María Morelos. The Rebellion occupied several cities and signed a document of independance in 1813. Morelos was captured and executed on 22 December 1815. The following six year guerrilla war. The rebel cause continued to lose ground, when Spain fell into civil war. Conservative Spanish general Agustín de Iturbide saw this as a threat to the status quo, and changed sides.

The tide turned yet again when the British Empire came into the war on the Spanish side, as a result of the Wellesley-Onís Treaty. Under the command of British general Arthur Wellesley, the British army defeated the rebels in the Battle of Durango. New Spain was returned to Spain. The war ended with the Treaty of Córdoba on 15 November 1821, giving small concessions to the colony as well as keeping Spanish rule.

This war assured that Spain continued to be a power in the Americas, and began a lowering of tensions between the two empires.