He was made a permanent field marshal on 25 March, and raised to the rank of count on 2 April. Caxias ran for a Senate seat, and being among the three candidates with the most votes, he was selected by the Emperor in late 1845 as the senator representing Rio Grande do Sul. He took his Senate seat on 11 May 1846. Conservatism Platine War After years in opposition in the parliament, in September 1848, the Party of Order was called upon by Pedro II to form a new cabinet. The saquarema cabinet was composed of men with whom Caxias had close relationships, among them Eusébio de Queirós, who had helped him bring order to the streets of Rio de Janeiro in the late 1830s. Caxias was now a wealthy planter who owned slaves and was very much a part of the landed aristocracy that formed the backbone of the Party of Order. With the help of his wealthy mother-in-law, he purchased his first property—a coffee farm—in 1838. He acquired more lands in 1849, further expanding his plantation. Due to growing international demand, coffee had become the most valuable export commodity for Brazil. In 1851, Juan Manuel de Rosas, dictator of the Argentine Confederation, declared war on Brazil. Caxias was appointed commander-in-chief of the Brazilian land forces. The Minister of Foreign Affairs, Paulino Soares de Sousa (later Viscount of Uruguai), forged an anti-Rosas alliance between Brazil, Uruguay and rebel Argentine provinces. When Paulino Soares asked who should be appointed as Brazil's representative among the allied forces, Caxias suggested Honório Hermeto. Honório Hermeto, who had been ostracized by his peers after his fall in 1844, was the saquarema closest to Caxias. An army commanded by Caxias crossed into Uruguay in September 1851. The allies decided to divide their forces into two armies: a multinational force that included a single Brazilian division, and a second army composed entirely of Brazilians under Caxias. Against the wishes of Honório Hermeto, Caxias chose Manuel Marques de Sousa (later Count of Porto Alegre) to lead the former force. Caxias met and befriended Marques de Sousa, who had served under his command in the War of the Ragamuffins, during his trip to Rio Grande do Sul in 1839. The Brazilian division, led by Marques de Sousa, along with Uruguayan and Argentine rebel troops, invaded Argentina. On 3 February 1852, in the Battle of Caseros, the allies defeated