Throughout the entirety of the Populist Republic, struggles over control of Brazil's national political scene prompted interventions from Brazil's military, whom the Constitution of 1946 had named the guarantor of law and order. Almost every presidential election or term -- with the exception of Eurico Gaspar Dutra, himself a member of the Brazilian Army -- summoned at least the threat of military action. In 1954, the military forced the resignation of Getúlio Vargas. Likewise, Juscelino Kubitschek's election in 1955 prompted serious rumors of a military overthrow.

Janio Quadros’ abrupt resignation of the presidency on August 25, 1961 prompted a serious crisis of governance in Brazil, with the military split between its longstanding goal of political stability one the one hand, and on the other, its deep mistrust of Quadros’ successor, Vice President João Goulart. The presidency of Goulart, or Jango as he is more commonly known in Brazil, faced opposition from the military, as well as mounting pressure from civilians such as Francisco Julião’s Peasant Leagues and government officials such as Leonel Brizola, whose opponents saw them as sympathetic to communism.

As Jango’s political support crumbled, rival groups in Brazil positioned themselves for a seemingly inevitable and drastic change in government. Ever anxious to guarantee pro-American, anti-Communist government in Brazil, the United States made common cause with its longtime allies in the Brazilian military. Led by General Humberto Castello Branco, by 1964 this conservative segment of the military had made clear its intentions to overthrow Jango's government. In response, the United States launched Operation Brother Sam, a plan to lend logistical support to the Brazilian military’s effort to take control of the Brazilian government. In the end, additional material support proved unnecessary to complete Jango's ouster. On March 31, 1964, Brazil's military once again put its constitutional powers into action, put an end to the Fourth Republic, and began a 24-year period of military dictatorship.

Key figures

• Castelo Branco, Humberto de Alencar, 1900-1967
• Gordon, Lincoln
• Goulart, João, 1918-1976
• Quadros, Jânio, 1917-1992

Key groups

• Instituto Brasileiro de Ação Democrática
• Instituto de Pesquisas e Estudos Sociais (Brazil)

Key subjects

• Brazil--History--Revolution, 1964