Paraguay took the initiative during the first phase of the war: invading Mato Grosso in the north on 14 December 1864,[1]: 25  Rio Grande do Sul in the south in early 1865, and the Argentine province of Corrientes.

[1]: 26  The Brazilian garrison of 154 men resisted for three days, under the command of Lieutenant Colonel Hermenegildo Portocarrero (later Baron of Forte Coimbra).

This detachment, led by Major Martín Urbieta, encountered tough resistance on 29 December 1864 from Lieutenant Antônio João Ribeiro and his 16 men, who were all eventually killed.

The second Paraguayan column, formed from some of the 4,650 men led by Colonel Francisco Isidoro Resquín at Concepcion, penetrated into Mato Grosso with 1,500 troops.

In January 1867, Colonel Carlos de Morais Camisão had assumed command of the column after the deaths of Drago and Galvão.