The Paraguayans, led by the Marshal of the Republic Francisco Solano López, retaliated by attacking the Matto Grosso on 15 December 1864 and later declared war against Argentina on 23 March 1865. The "Blanco Government" was toppled and replaced by a "Colorado Government" under General Venancio Flores on 22 February 1865 and afterwards, the Argentine Republic, the Empire of Brazil and the Republic of Uruguay signed the Secret Treaty of the Triple Alliance against the Paraguayan Government, on 1 May 1865.