The Battle of Caseros () was a military engagement fought near the town of El Palomar, Buenos Aires Province, Argentina, on 3 February 1852, between the Army of Buenos Aires commanded by Juan Manuel de Rosas and the Grand Army (Ejército Grande) led by Justo José de Urquiza. The forces of Urquiza, caudillo and governor of Entre Ríos, defeated Rosas, who fled to the United Kingdom. This defeat marked a sharp division in the history of Argentina. As provisional Director of the Argentine Confederation, Urquiza sponsored the creation of the Constitution in 1853, and became the first constitutional President of Argentina in 1854.
Background
Argentine Civil Conflict
From 1814 onwards, Argentina faced on serious internal challenges, resulting from disagreements over the proper form of government. This resulted in a series of civil wars that destabilized the young nation.
End of the Anglo-French Bloc
A British-French alliance had stymied Argentine leader Juan Manuel de Rosas and his ally Manuel Oribe from taking the Uruguyan capital of Montevideo by blockading the Rio de la Plata. This began a long and arduous siege. However, as Rosas consolidated his position in the interior, the Europeans began to doubt the ability of the defenders of Montevideo to resist the siege, and thus began a series of agreements, culminating in the end of the blockade in the Arana–Southern Treaty. Emboldened, Rosas decided to tighten his grip on the city by outlawing any up to that point tolerated trade with the city, which angered those who relied on it, among them the governor of Entre Rios, Justo José de Urquiza.
Urquiza's Pronunciamiento
The treaty came as a lucky break for Rosas as he began to face down a new threat: the Empire of Brazil, who felt threatened by the leverage Rosas might have over them with control over Montevideo and Uruguay in general. Rosas sent Urquiza to study the front and make preparations for a war with Brazil. Instead, Urquiza, suspicious that the warmongering was a ploy to delay the writing of an Argentine constitution, began to make plans of his own and negotiated loans from the Brazilians when he decided to rebel.
When he felt it was most opportune, he released a statement from Concepción del Uruguay known as his Pronuniciamiento, calling for the resignation of Rosas. He began gathering troops, approximately 10,000 horsemen in total before making his next move.
The Uruguay Campaign
In a joint treaty with Brazil and the Montevideo government, Urquiza's Entre Rios government declared their intention to first expel Oribe from Uruguay and then establish free elections in Argentina. They also agreed to come to the others' defense if Rosas decided to declare war on them.
With his allies in Corrientes, Urquiza crossed into Uruguay while a Brazilian force invaded from north. Facing such overwhelming odds, Oribe did not put up a fight, and instead signed an agreement allowing him to extricate himself peacefully. The Brazilians imposed a harsh price on the Montevideo government for their help, annexing a northern strip of the nation and forcing them to declare Brazil the guarantor of Uruguyan independence.
The Campaign of the Ejército Grande
Finally, the allies turned on Rosas, declaring war on his government. In compliance with the treaty, Urquiza led a joint army and crossed Morón creek, positioning his forces in Monte Caseros.
Rosas's response up to this point had been lethargic and overly cautious, and this time was no different. Leadership was confused as his appointed commander Angel Pacheco resigned due to contradictory micromanagement and incompetence on Rosas's part. In the end, Rosas, an aging politician more suited to administration than warfare, decided to take personal command of the battle. Because he was not an experienced or skilled commander, he made no effort to scout for a good battle position, and simply waited for the allies to come to him.
The battle
The Defenders (Rosistas)
Rosas' forces consisted of some 10,000 infantry troops, 12,000 cavalrymen and 60 guns. Among his captains were Jerónimo Costa, who defended Martín García island from the French in 1838; Martiniano Chilavert, a former opponent of Rosas who defected when his fellows allied themselves with foreigners; Hilario Lagos, veteran from the campaign against the Indians of 1833.