The Vargas regime's relationship with Nazi Germany and Fascist Italy wavered throughout the 1930s. Foremost among the concerns of the staunchly nationalist Getúlio Vargas were the sizable populations of Italian immigrants in the state of São Paulo and Germans in the southern states of Paraná, Santa Catarina, and Rio Grande do Sul, whom Vargas saw as a potential fifth column that might one day work alongside their countrymen in Argentina to overthrow the Brazilian government. Germany's support for Nazi party activity in southern Brazil and Argentina only increased Vargas' suspicions, resulting in a campaign against the Nazi party in Brazil and the expulsion of German ambassador Karl Ritter in 1938. Despite these domestic fears, the Vargas regime saw neutrality as a means of maximizing economic relations with the Axis powers. Contrary to its counterparts in the League of Nations, the Vargas government hoped to use the Italo-Ethiopian War from 1935-1936 to increase exports to Italy, and in 1936 concluded a secret economic agreement with Mussolini. Brazil likewise maintained friendly relations with Germany, and secured an advantageous arms contract with the Nazi government the same year it expelled Germany's diplomat. As late as 1941, the Axis powers felt confident they had an ally in Brazil.

Officials in the governments of both Brazil and the United States saw each other as crucial allies against any threat the Axis Powers might pose to South America, though each country disagreed as to the endangered territory. The United States was most concerned with the northeastern corner of Brazil, known as the Natal bulge, which could be used to disrupt shipping and transport by air or sea to several theaters of war. Brazil, however, saw the greatest danger in its southern border with its rival Argentina. Despite their opposing interests at times, both Brazil and the United States were careful not to fall out of favor with each other. Mutual visits from each country’s top military officials helped establish a sense of common support. On May 25, 1939, George C. Marshall arrived in Rio de Janeiro to raucous applause. In July of the same year, Brazilian General Goes Monteiro toured United States military installations and was received warmly everywhere he went. Foreign Minister Oswaldo Aranha's five-week visit to the United States earlier in the year secured Brazil substantial lines of credit, loans, and technical assistance for the development of Brazilian rubber and mining industries. On September 26, 1940 the United States and Brazil signed agreement for the financing and construction of the Volta Redonda steel mill. By the end of 1940, Brazil had privately resolved to throw its lot in with the Allies.

The attack on Pearl Harbor on December 7, 1941 brought World War II to the Western Hemisphere. On January 28, 1942, the final day of the Third Meeting of Ministers of Foreign Affairs of the American Republics, also known as the Rio Conference, Brazil joined Ecuador, Peru, Paraguay, and Uruguay in severing diplomatic relations with the Axis powers. In exchange for this break in diplomacy, Brazil pressed the United States for drastic increases in military and economic assistance, and on March 3, 1942, the United States signed what was to be the most comprehensive assistance program the country had ever undertaken in Latin America. With Brazilian neutrality gone, the United States government no longer hid the operations of its "springboard to victory", Parnamirim Airfield in Natal, Rio Grande do Norte. Built and operated in conjunction with Pan American Airways, Parnamirim was to become one of the busiest and largest military airfields of the war. After a German U-boat sank five Brazilian ships off the coast of Bahia, Brazil officially declared war on the Axis powers, becoming one of only two Latin American nations to send troops to fight in World War II, and the only Latin American country to send troops to fight in Europe. Beginning on July 18, 1944, under the command of General Mascarenhas de Moraes, the 25,000-strong Brazilian Expeditionary Force (Força Expedicionária Brasileira or FEB in Portuguese) joined the Italian campaign, most notably at Monte Castello. Given Brazil's relative poverty among the Allied powers, the impossibility of raising such a sizable expeditionary force was likened to that of a snake learning to smoke, leading to the FEB's nickname as the Smoking Cobras (Cobras Fumantes in Portuguese). Upon its return to Brazil in 1945, the FEB, which included Brazil's future military dictator Humberto de Alencar Castello Branco, was almost immediately disarmed and demobilized by a Vargas regime ever fearful of military insurrection. 

Key events  

• Meeting of Consultation of Ministers of Foreign Affairs of American States (3rd : 1942 : Rio de Janeiro, Brazil)
• World War, 1939-1945--Campaigns--Italy

Key figures 

• Monteiro, Pedro Aurélio de Góes

Key groups

• Brazil. Exército. Força Expedicionária Brasileira, 1944-1945.
• United States. Office of War Information.

Key places 

• Castello del Monte (Italy)
• Parnamirim Air Base (Brazil)

Key subjects 

• World War, 1939-1945--Brazil. 
• World War, 1939-1945--Campaigns--Brazil
• World War, 1939-1945--Personal narratives, Brazilian
• World War, 1939-1945--Regimental histories--Brazil
• World War, 1939-1945--South Atlantic Ocean