Mauritania, Niger, Somalia, Tanzania and Zambia. It includes 187 million inhabitants in 2019 (2.4% of the world population), and will count 931 million by 2100, that is to say, 8.6% of the world population (according to estimates and medium-variant) (United Nations 2019a).
In summary, in a few decades, based on past and current demographic trends, global demographic change has been radical and a complete geopolitical redistribution is underway, according to the United Nations’ medium-variant (United Nations 2019a).
Table 1.2. Groups of countries per demographic transition and population in 2019, 2030 and 2100 (in billions of inhabitants)
(source: World Population Prospects 2019 (estimates and medium-variant); United Nations 2019a)
| Complete demographic transition by 2019 | Complete demographic transition by 2030 | Complete demographic transition between 2030 and 2100 | |
| Group 1 | 1.1 billion Europe, North America, Oceania | 1.2 billion | |
| Group 2 | 2.4 billion Japan, China, Republic of Korea, Democratic People's Republic of Korea, Chile, Brazil, Colombia, Uruguay, Western Asia, Bangladesh, Iran, Sri Lanka | 2 billion | |
| Group 3 | 2.5 billion | India, Southeast Asia7, Latin America8, Libya, Tunisia, Mauritius, Réunion Island, Cape Verde | 2.1 billion |
| Group 4 | 0.550 billion | 0.860 billion Pakistan, Cambodia, Laos, Philippines, Algeria, Morocco, Bolivia, Guatemala, Haiti, Panama, Paraguay, Botswana, South Africa | |
| Group 5 | 0.557 billion | 1.7 billion Sub-Saharan Africa9 | |
| Group 6 | 0.187 billion | 0.931 billion |
Note: The definition of a complete demographic transition considers a life expectancy of over 70 years and a total fertility lower than 2.1 children per woman. We only counted the most populated countries in 2019.
If we add to the main countries that completed their demographic transition in 2019 (groups 1 and 2), those of the third group (ending in 2030), this set comprises 78% of 2019’s world population (6.1 billion). But this will significantly decrease: by 2100, it will bring together 5.3 billion inhabitants, or 48% of the world population (estimates and medium-variant) (United Nations 2019a). Indeed, the countries which are currently completing their demographic transition will experience a modest population growth, with an older age structure.
However, the population of the main countries where the demographic transition is still “awaiting completion” (groups 4, 5 and 6), which reached 1.3 billion and 16% of the world’s population in 2019, will rise to 3.5 billion inhabitants by 2100 and its proportion will double (32%). Its population growth will be high due to the gap between the decline in mortality and the decline in birth rates, and a young age structure.
1.4. The demographic transition in the world
The demographic transition started in the mid-18th century in Europe, prompting two centuries of extraordinary progress reducing the mortality rate, because of the control of epidemics and famine. In France, between 1780 and 1840, life expectancy rose from under 30 to over 40 years of age, and from 1880 to 1940, from 43 to almost 60 years. Infant mortality also fell sharply. Advances in mortality did not take place in all European countries at the same time, or at the same pace. They were interrupted by wars (War of 1870, First World War) and the flu of 1918. Medical discoveries, in particular those of Pasteur on the microbial origin of infectious diseases, health progress and a rise in the standard of living, significantly contributed to reducing epidemics and food shortage (Vallin 2003, pp. 9–14). In addition, the increase in life expectancy continued to soar, reaching over 80 years between 2015–2020 (in Australia, Canada, South Korea, Europe, Japan, Singapore, etc.). In 2019, at a global level, life expectancy for both sexes was 72.3 years: in developed countries, it was 79.2 years, and 72 years in developing countries (United Nations 2019a, Table A.28).
After 1870, the decline in fertility in Europe started later than that of mortality, falling from almost five children to around two or three children per woman on the eve of the Second World War. Only France started limiting births in the mid-18th century, more than a century before other European countries (Festy 1979). The gap between the dates of the beginning of the decline in mortality and that in fertility was responsible for a strong population growth. Thus, the population of England and Wales increased from 6.5 million in 1750 to 42 million in the early 1940s (Vallin 2003, p. 27).
In the mid-20th century, the demographic transition spread to Asia and Latin America, with mortality declining after 1950, followed by fertility circa 1970 (Chesnais 1986a). The decrease in mortality was further accelerated by the effectiveness of health policies resulting from previous experiences in developed countries (Omran 1971). For four decades, between 1940 and 1990, the birth rate greatly exceeded the crude death rate, leading to strong population growth, higher than 2% per year. This figure had never been reached in Europe or in Japan (Chesnais 2002, p. 458). Finally, during the second half of the 20th century, the decline in fertility became widespread. Contrary to what happened in Europe, “the explosion of the Third World” (Vallin 2003, p. 60) resulted in the implementation of birth control policies, thus rapidly reducing fertility. As Vallin wrote, “there are few cases when one can say that the introduction of a birth control program is the main factor underlying a desired reduction in fertility” (Vallin 2011, p. 344). But he rightly emphasized that access is made easier, for couples and for women who wish to limit their births, when such programs exist (Vallin 2011, p. 344).
1.4.1. The factors which can explain demographic transitions
To explain the decline in mortality in Europe since the end of the 18th century, Abdel Omran (1971) proposed the theory of epidemiological transition, or the passage from an old mortality regime (the “age of pestilence and famine”), through a transition period of a “decline in pandemics”, to finally reach the last age of “degenerative” and “societal” diseases (Omran 1998). Then appeared the more general concept of “health transition” (Meslé and Vallin 2002). During this period, medical advances for reducing infectious and cardiovascular diseases were accompanied by the development of food, agriculture and education, as well as an improvement in the living standards, the establishment of a sanitation infrastructure (drinking water, sewers) and the development of health systems. But, within these dimensions, inequalities have widened, because the entire population does not have equal access to them (Meslé et al. 2011, p. 484).
In Europe, the delays in the age for marriage10 accompanied the secular decline in fertility, in the absence
