The War of Canudos was a conflict between the First Brazilian Republic and the residents of Canudos in the northeastern state of Bahia. It was waged in the aftermath of the abolition of slavery in Brazil (1888) and the overthrow of the monarchy (1889). The conflict arose from a millenarian cult led by Antônio Conselheiro, who began attracting attention around 1874 by preaching spiritual salvation to the poor population of the sertão, a region which suffered from severe droughts. Conselheiro and his followers came into attrition with the local authorities after founding the village of Canudos. The situation soon escalated, with Bahia's government requesting assistance from the federal government, who sent military expeditions against the settlement.

The First Brazilian Republic, also referred to as the Old Republic, officially the Republic of the United States of Brazil, refers to the period of Brazilian history from 1889 to 1930. The Old Republic began with the deposition of Emperor Pedro II in 1889, and ended with the Brazilian Revolution of 1930 that installed Getúlio Vargas as a new president. During the First Brazilian Republic, Brazil was dominated by a form of machine politics known as coronelism, in which the political and economic spheres were dominated by large landholders. The most powerful of such landholders were the coffee industry of São Paulo and the dairy industry of Minas Gerais. Because of the power of these two industries, the Old Republic's political system has been described as "milk coffee politics."