The Brazilian monarchy had been in trouble for years before November 1889. The Paraguayan War had strengthened the army and weakened civilian authority. Emperor Pedro II's health was declining, and his successor would be his daughter Princess Isabel, whose husband had a controversial reputation. The Church had soured on the government. The final trigger was a rumor that Deodoro da Fonseca, a popular marshal sympathetic to military reformers, was about to be arrested. Allies pressed him to act first. He did, leading troops to depose the cabinet in the capital. Whether he declared the Republic that same day or only intended to install a new prime minister is disputed by historians; it is unknown what exactly Deodoro meant to accomplish. But the republicans around him pushed the situation toward full regime change, and by evening the Emperor was heading into exile. Brazil's monarchy had lasted 67 years. Its successor lasted 41.

The First Republic's central political mechanism was an informal agreement between the oligarchs of Sao Paulo, who grew coffee for export, and those of Minas Gerais, whose dairy industry dominated their state. The two largest economies alternated the presidency between them. The arrangement was informal but iron-clad: each succeeded the other through elections that were stage-managed to produce the expected result. Outside these two, the states of Rio Grande do Sul, Bahia, and Pernambuco mattered less but occasionally had to be placated. At the local level, politics ran on coronelismo, a system in which local bosses, called coronels after the National Guard rank, delivered the votes of their followers to whichever candidate promised them the most favors. Rural voters were pressured, bribed, or simply told how to vote, and when all else failed, the verification commissions in Congress could simply rewrite the results. This was constitutional democracy in name. In practice it was oligarchic rule at every level.

The peace of oligarchic rule produced its own resistance. In 1896, a wandering religious leader named Antonio Maciel built a settlement at Canudos in the Bahian backlands that drew thousands of poor followers. The Bahian governor attacked the community over a minor dispute about timber. His expedition was defeated. A second expedition was defeated. A third was defeated. Finally, in 1897, General Artur Oscar led 8,000 men to raze the settlement. The war killed thousands of Brazilian backlanders, whose poverty and religious intensity had been miscast as monarchist rebellion. Canudos was one of several uprisings that punctuated the First Republic: the Federalist Rebellion of 1893 to 1895 in the south, the Vaccine Revolt of 1904 in Rio de Janeiro, the Revolt of the Whip of 1910 in the navy, the Juazeiro Sedition of 1914, and the Contestado War from 1912 to 1916 between settlers and landowners. Each revealed a different crack in the oligarchic facade.

Brazil stayed out of World War I until 1917, when German submarines sank Brazilian civilian ships off the French coast. President Venceslau Bras declared war on October 26, 1917, partly to distract from domestic corruption and partly because external threats rallied national sentiment. Brazilian contribution was modest: medical staff, sergeants, officers, a small air contingent attached to the French Army and British Royal Air Force, and a naval fleet joining Allied operations in the Mediterranean. The armistice came before Brazil could carry out a larger plan. But the war changed the economy. With Britain unable to export, Brazilian manufacturers seized the opening. Industrial enterprises grew from about 3,000 in 1908 to nearly 9,000 by 1918. The new manufacturing class and the growing urban middle class had interests that did not align with the coffee oligarchs, and the politics of cafe com leite started to show its age.

The Great Depression crushed global coffee demand and exposed the vulnerabilities the Republic had papered over. In the 1930 election, outgoing President Washington Luis from Sao Paulo violated the alternation rule by backing another Paulista candidate, Julio Prestes, instead of a Mineiro. Minas Gerais, Paraiba, and Rio Grande do Sul united in the Liberal Alliance behind Getulio Vargas. Prestes officially won with 57.7 percent, but Vargas and his allies refused to accept the result. When Liberal Alliance vice-presidential candidate Joao Pessoa was assassinated in Recife on July 26, 1930, the country ignited. On October 3, revolutionary forces began moving in Rio Grande do Sul. Eight northeastern state governments were deposed within days. Federal generals and an admiral finally deposed Washington Luis themselves on October 24 to prevent a full civil war. On November 3, 1930, at 3 p.m., the junta handed the presidential palace to Getulio Vargas. The 1891 Constitution was abrogated. The National Congress was dissolved. Vargas would rule Brazil, in various forms, for 15 years directly and for a brief return in the 1950s, ending the Old Republic and beginning the Vargas Era. Coffee with milk had kept the coffee interests on top for 41 years. The 1930s would be about industrializing a country.