Political map of South American nations 13 December 1864 (Outbreak of the Paraguayan War): In 1864 Brazil intervened in Uruguay in support of the liberal Colorado Party (Uruguayan War), prompting Uruguay's governing Blanco Party to call on Paraguay for support. Confident in his larger and better-equipped military, and desirous of settling his country's numerous unresolved border disputes, Paraguayan President Solano López declared war on Brazil (Paraguayan War) in December.