did not launch this force on Argentina, but on Brazil. Alleged maltreatment of Brazilian nationals by the Uruguayan Blancos was a longstanding Brazilian grievance and in April 1864 political agitation brought Brazilian anger to the boil. In May 1864 Brazil sent a diplomatic mission to Uruguay to demand reparations, accompanied by a naval squadron; Brazilian troops massed along the border. On 30 August 1864 Paraguay warned Brazil against military action in Uruguay, but this was ignored: the Uruguayan War began. In November 1864, Paraguay fired upon and seized the Brazilian government ship Marqués de Olinda as it was steaming up the River Paraguay on its routine monthly voyage to the Mato Grosso. It proved to be carrying military stores. Paraguayan armies proceeded to invade the Brazilian province of Mato Grosso. On 14 January 1865, the Paraguayan government asked Argentina for permission to attack Brazil across the Corrientes Province, which was refused. On 13 April, Paraguayan ships fired upon and seized two Argentine naval vessels moored in the Argentine port of Corrientes and the Paraguayans proceeded to invade the province itself. Paraguay had now made war on the much more populous Empire of Brazil, on Argentina (also more populous), and threatened the Colorado faction of Uruguay (which by now had come into power). The three countries had been accustomed to thinking about Paraguay as a backward upstart and were outraged. Their foreign ministers met in Buenos Aires and negotiated the Treaty of the Triple Alliance. Negotiations In March 1865, a change of government in Brazil had Liberal Party member Francisco Otaviano de Almeida Rosa sent on a special mission to the River Plate region. (Paraguay was at war with Brazil but had not yet attacked Argentina.) Some of his instructions were to bolster the Uruguayan government of the pro-Brazilian Venancio Flores, to see how Uruguay might co-operate in the war against Paraguay, and to stop the Argentine government from making any obstacles. The Paraguayan attack on Argentine territory (13 April) precipitated the Brazil-Argentina alliance so that the 40-year old Otaviano had to negotiate its terms on the spot, without specific instructions from Rio de Janeiro since there was no telegraph link with that capital. His general instructions had been that Paraguay should have to pay for the war, the Humaitá fortifications must be destroyed to guarantee freedom of navigation, and a boundary treaty must be signed with Paraguay according to certain