Battle of Cepeda ( 1859 ) The Battle of Cepeda of 1859 took place on October 23 at Cañada de Cepeda , Santa Fe , Argentina . The Republic of the Argentine Confederation army , led by " Federal " Justo José de Urquiza defeated the State of Buenos Aires forces , led by " Unitarian " Bartolomé Mitre . The battle in context . 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 instransigent 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 union " San 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 .