First Stages

By November 12, 1864, Solano López assessed that Brazilian intervention in Uruguay as a disdain to his country. He was also inclined to believe that neither Brazil nor Argentina took Paraguay's interests into account. As a result, he concluded that to play a more important role in the region, Paraguay would have to incur in an offensive foreign policy. With such objective, he was determined to support the Blanco government under Anatasio Aguirre.

By december 12, he declared war against Brazil and on the   16th , he launched a quickly attack by invading Mato Grosso province in the west of Brazil

The success of this operation led Solano Lopez to concluded that his forces were superior to his foes troops. He paid little attention to the fact that Paraguayan Troops were sent to a province poorly defended, far from the Uruguayan soil and with no strategic importance for  future war operations.

By the end of the year López decided to strike at Brazil's main force in the southern province of Rio Grande do Sul, isolating the empire forces in Uruguay from his base in Brazil. He gathered some of Paraguay's best troops under Colonel Antonio de La Cruz Estigarribia to cross the Argentine province of Corrientes in order to attack the Brazilian positions. On March 18, 1865 believing that Argentina would remain at least neutral, since many Argentine provinces were against an alliance with Brazil, the Paraguayan Army rushed into Corrientes expecting local strongmen to join them. Instead, the action set the stage for the May 1865 signing by Argentina, Brazil, and Uruguay of the Treaty of the Triple Alliance.

Under the treaty, these nations vowed to destroy Solano López' goverment.;

Paraguayan officer. Source; National Library (Brazil)

Officer and soldier of the Imperial Army. By Hendrik Jacobus Vinkhuijzen, 1867. Source: http://pt.wilkipedia.org/wiki/Guerra_do_Paraguai

Riachuelo