How did migration from other parts of Brazil increase Rio de Janeiro's population?

Historically, domestic migration from other parts of Brazil was a primary driver of population growth in Rio de Janeiro, at times accounting for two-thirds of the city's increase in a single year. By 1960, nearly half of the city's population consisted of internal migrants, primarily born in the states of Rio de Janeiro, Minas Gerais, and Espírito Santo.1

This migration significantly fueled the expansion of the metropolitan region, particularly during the mid-20th century. Between 1940 and 1960, the suburban population more than tripled, driven more by these internal movements than by natural population increase. While the transfer of the national capital to Brasília in 1960 caused the rate of growth in the city proper to slow, internal migrants continued to be directed toward other municipalities within the metropolitan region. These suburban areas, such as those in the Baixada, grew tremendously after being linked to the city by rail, transforming from small rural centers into densely populated urban zones.231