[1] About 55,000 persons were mostly transferred from drought-stricken northeast areas and contributed to the second rubber boom in Brazil.
[2] Each migrant signed a contract with SEMTA which offered a small salary for the worker during their transport to the Amazon region.
After being recruited, the volunteers were placed in specially-built housing, under strict military watch, and then sent into the Amazon, on trips which could last two to three months.
They died of malaria, yellow fever, and hepatitis,[4] and were attacked by animals such as jaguars, snakes, and scorpions.
The Brazilian government also did not fulfill its promise to return the "rubber soldiers" to their homes at the end of the war as heroes and with housing comparable to that of the military.