An unintended consequence of the attack on Melo was that Paraguay declared war on Brazil in late 1864. The Paraguayans invaded the provinces of Mato Grosso (present-day Mato Grosso do Sul) and Rio Grande do Sul. José Luís served in the Siege of Uruguaiana which resulted, in September 1865, in the surrender of an entire Paraguayan army which had taken the Brazilian town of Uruguaiana. On 22 March 1866, José Luís was given command of the 2nd cavalry division, a part of the 1st army corps. He fought in the Battle of Estero Bellaco on 2 May and in the First Battle of Tuyutí on 24 May. At Tuyutí José Luís was shot in the face with the bullet's trajectory entering one cheek and exiting through the other. He was left with hideous scars that made him look like he had a grim smile in his face. Tall and lean, José Luís seemed unpleasant at first glance, an impression that the disfigurement only worsened. He was actually a kind and warm person, according to historian Gustavo Barroso, who as commander knew how to impose a strict discipline without hurting the pride of his subordinates.