Question: What was the reason for Brazil's population increase between the years of 1940 and 1970?
About the article "Brazil", section "Demographics".

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Following contact with Brazilians in 1946, a population of 4,000 at the time was eventually reduced to 120 after Brazil's second rubber boom and the construction of the Trans-Amazon highway in 1970.
Further colonization of the Amazon basin led to the spread of diseases that the Parintintin were not prepared for.  
This list here of the 115 most populous cities is based on the population of the municipality where the city is located, rather than its metropolitan area.
IBGE estimates of 2010 State capitals are in bold.
Second Rank* is by capitals and non-capitals.
Palmas is the only state capital not listed.
Brazil's population, as recorded by the 2008 National Household Survey, was approximately 190 million inhabitants (22.31 inhabitants per square kilometer), with a proportion of men and women of 0,95:1 and 83.75% of the population defined as urban.
The population is heavily concentrated in the Southeast (79.8 million) and Northeast (53.5 million), while the two wider regions, the Midwest and North, which form 64.12% of Brazil, have a total of just 29.1 million inhabitants.
Brazil's population increased significantly between 1940 and 1970, due to a decline in mortality, although the birth rate has also declined slightly in the past period.
In the 1940s the rate of annual population growth was 2.4%, rising to 3.0% in 1950 and remaining at 2.9% in 1960, life expectancy rose from 44 to 54 years and 72, 6 years in 2007.
The rate of population increase has been declining since 1960 of 3.04% per annum between 1950–1960 to 1.05% in 2008 and expected to drop to a negative value of −0.29% in 2050, thus completing demographic transition.
The major metropolitan areas of Brazil are São Paulo, Rio de Janeiro and Belo Horizonte – all in the Southeast – 19.5, 11.5 and 5.1 million inhabitants respectively.
Almost all capitals are the largest cities in their states except Vitória, capital of Espirito Santo, and Florianópolis, the capital of Santa Catarina.
There are also non-capital metropolitan areas in the states of São Paulo (Campinas, Santos and Paraíba Valley), Minas Gerais (Steel Valley), Rio Grande do Sul (Sinos River Valley), Santa Catarina (North/Northeast) and (Itajaí River Valley) and Ceara (Juazeiro do Norte - Cariri Metropolitan Region). 
Population growth.
The population was relatively stable in the second half of the 19th century (lowest value: 137; highest value: 156).
The all-time high came in 1900, when the population reached 276.
However, many of these were laborers working on the Abula train line.
For the same reason (construction) the population was above average in 1970.
Between 1900 and 1930 the population rose slightly, remained stable for two decades, and then fell in the 1980s.
Since then the population has oscillated about 150.
Alvaschein has a population (as of ) of .
, 4.1% of the population was made up of foreign nationals.
Over the last 10 years the population has decreased at a rate of -17.1%. 
The population of Brazil, as recorded by the 2008 PNAD, was approximately 190 million (), with a ratio of men to women of 0.95:1 and 83.75% of the population defined as urban.
The population is heavily concentrated in the Southeastern (79.8 million inhabitants) and Northeastern (53.5 million inhabitants) regions, while the two most extensive regions, the Center-West and the North, which together make up 64.12% of the Brazilian territory, have a total of only 29.1 million inhabitants.
The first census in Brazil was carried out in 1872 and recorded a population of 9,930,478.
From 1880 to 1930, 4 million Europeans arrived.
Brazil's population increased significantly between 1940 and 1970, because of a decline in the mortality rate, even though the birth rate underwent a slight decline.
In the 1940s the annual population growth rate was 2.4%, rising to 3.0% in the 1950s and remaining at 2.9% in the 1960s, as life expectancy rose from 44 to 54 years and to 72.6 years in 2007.
It has been steadily falling since the 1960s, from 3.04% per year between 1950 and 1960 to 1.05% in 2008 and is expected to fall to a negative value of –0.29% by 2050 thus completing the demographic transition.
In 2008, the illiteracy rate was 11.48% and among the youth (ages 15–19) 1.74%.
It was highest (20.30%) in the Northeast, which had a large proportion of rural poor.
Illiteracy was high (24.18%) among the rural population and lower (9.05%) among the urban population.
  Moreira was voted the number one percussionist in ""Down Beat" Magazine's Critics Poll" for the years 1975 through 1982 and most recently in 1993.
In September 2002, Brazil's President Fernando Henrique Cardoso added Moreira and Purim to the "Order of Rio Branco", one of Brazil's highest honors.