On the aftermath of the Battle of Caseros, following the San Nicolás Agreement that convened the Constitutional Congress of 1853, the Province of Buenos Aires seceded from the Argentine Confederation and established an independent State, the State of Buenos Aires. However, the Confederation still depended on the port of Buenos Aires for its foreign trade. Moreover, Urquiza's policy of seduction towards the rebel Province had failed, and the secessionist State elected as its Governor the radical autonomist and Unitarian Valentín Alsina in 1857. On April 1, 1859, following the assassination of former San Juan Province Governor Nazareno Benavídez by a presumed Buenos Aires agent, the Confederation Congress passed a law by which the President Justo José de Urquiza was obliged to "peacefully reincorporate the dissident province of Buenos Aires", but -if this was not possible-, he was allowed to make use of the national army to accomplish that purpose. The Government of Buenos Aires interpreted that law as a formal declaration of war. In May, the Legislature of the State allowed the Governor to repel any military aggression with the Province's militia. Colonel Bartolomé Mitre, in charge of Buenos Aires troops, was ordered to attack Santa Fe Province while the Navy was sent to blockade Paraná, the capital city of the Confederation. Given the imminence of conflict, Brazil, Paraguay, the United States and the United Kingdom tried to prevent it by diplomatic means. The neighbouring country of Paraguay sent a young Francisco Solano López as a plenipotentiary minister to intercede in the emergency. But every attempt at the pacific resolution of the conflict failed since Buenos Aires demanded Urquiza's resignation as President, and the Confederation wouldn't comply to that. The army of the Confederation met Buenos Aires forces at Cañada de Cepeda, north of Pergamino. After some tactical movements, both forces clashed on the afternoon of October 23. By dusk, Mitre knew his forces were defeated, so the bonaerense army retired towards San Nicolás de los Arroyos, from where they embarked back to Buenos Aires.
Consequences
Urquiza did not enter Buenos Aires City and camped instead at the neighbouring town of San José de Flores to carry on with the negotiations. Governor Valentín Alsina was forced by his own allies to left office given his intransigent position towards the reintegration of Buenos Aires to the Confederation. On November 11, on the mediation of Francisco Solano López of Paraguay, Buenos Aires and the Argentine Confederation signed the national unionSan José de Flores Pact, by which Buenos Aires was de iure reincorporated into Argentina, allowing the Province certain privileges that would eventually led to the Battle of Pavón and the growing predominance of Buenos Aires Province.
