Military planners in the late 1920s characterized the army as the central agent of Brazilian national unity and greatness. They believed that economic development, military preparedness, and national power were linked tightly. The national territory held immeasurable resources that had to be protected from covetous foreigners until Brazilians could exploit them. They pointed to Japan and Argentina as examples of countries building military and economic power simultaneously. Reformist officers (called "Young Turks" after the military reformers of Turkey) thought that the lack of national cohesion was a far greater threat to Brazil than was any foreign threat. The army, in their view, was the only instrument to hold the country together by being a school of citizenship, and by teaching the superiority of the collective over individual good in sacrifice for the motherland. Meanwhile, Brazilians of all classes fled from military service, and draft dodging was chronic.

Even so, obligatory military service resulted in the physical expansion of the army, which eventually gave it the ability to intervene in politics and in society more profoundly than in the past. To give the army a local image while eliminating the expense and supervisory burden of transporting draftees to distant training camps, garrisons were established in every state to train them. The new system also required expanding the number of personnel in the army (18,000 to 25,000 in 1916-17, 30,000 in 1920, 48,000 in 1930, 93,000 in 1940); indeed, during the Old Republic, it grew 52 percent faster than did the rapidly growing population.

In the 1920s, an intense struggle for control of the army was in part motivated by conflicting ideas of what the institution's role was to be in the increasingly consolidated Brazilian nation-state. The German-trained Young Turks sought modernization. After 1919 the French Military Mission also encouraged professionalization and enhancement of the army's self-image as the central institution of the Brazilian state. By 1929 the state had intensified its centralizing powers by expanding federal ownership of the country's railroads, shipping lines, ports, and banks. In the coffee-dominated economy, the federal government controlled coffee marketing and sought to influence world coffee prices. However, some officers were troubled by who was running the state and army during the presidencies of Venceslau Brás Pereira Gomes (1914-18), Delphim Moreira da Costa Ribeiro (acting, 1918-19), and Epitácio da Silva Pessôa (1919-22).

The lieutenants' rebellions (tenentismo --see Glossary) of the 1920s were complicated in that they involved a minority of officers who were as much in revolt against the army hierarchy as against the central government. There was to be no amnesty, and so faced with either giving up their careers or continuing to conspire, the tenentes chose the latter. The result was the 1924 uprising in São Paulo and Rio Grande do Sul, which led to the retreat of the tenentes into the interior and the long campaign of the Prestes Column, named after the romantic revolutionary Luis Carlos Prestes, across Brazil until it gave up and entered Bolivia in 1927. In that decade, many of the best of the officer corps became rebels to save their careers and to save the army from corrupt officers. Thus, during the 1920s, the army institution played a conservative role, while a determined, talented minority of its officer corps pursued revolution.