 Barely a month later on 18 August 1851 , Juan Manuel de Rosas , dictator of the Argentine Confederation , declared war on Brazil , beginning the Platine War . Marques de Sousa had been warned by Caxias as early as 27 July 1844 of the possibility of an armed conflict between Brazil and its Platine neighbor . The government in Rio de Janeiro had prepared against the threat and formed an anti @-@ Rosas alliance consisting of Brazil , Uruguay and dissident Argentine provinces . Caxias , who had been appointed commander @-@ in @-@ chief of Brazilian land forces , placed Marques de Sousa at the head of the 2nd Brigade , part of the 2nd Division . The Brazilian army crossed into Uruguay in September 1851 . On 17 November , while the army was camped in the village of Santa Lucía near the Uruguayan capital , Marques de Sousa was promoted to a higher command , the 1st division . The choice was controversial , as there were two more senior and experienced officers next in line who were bypassed owing to their foreign birth . 
