In the growth of the population of Paris during the nineteenth century there were several decades in which 80 and even 90 percent of the population growth was due to the migratory balance, and since the immigrants were predominantly young, they also contributed to increase the global fertility rates (7) The relative figures of the urban population had a rapid ascending process until reaching already high percentages at the beginning of the XX: in Great Britain, 75% of the national total in 1911. Something similar happened in Spain, although with the well-known chronological lags (8).
In practically all European cases, it could be said that it is an urban growth directly related to the internal migration of each country. But international and intercontinental migrations also acquired a massive dimension from this moment and also gave rise to a strong growth of cities in the receiving areas.
Between 1800 and 1930, some 40 million Europeans left the Old Continent to go live in other countries (9). Between 1846 and 1932, 34.2 million immigrants arrived in the United States; to Argentina and Uruguay 7.1; to Canada 5.2; to Brazil 4.4; to Australia and New Zealand 3,4; to Cuba 0.9; and although some would later return to their countries of origin, the vast majority remained in their destination (10).
Almost all the American countries, plus Australia, New Zealand and some regions of Africa colonized by Europeans became areas of strong immigration in the 19th century, and received masses of immigrants of multiple nationalities.
In the United States, the arrival of immigrants (about 5 million until 1861 and then another 4 million between 1865 and 1880, of which at least three-quarters stayed in the country) led to the arrival of contingents of very diverse origin and cultures. Starting in 1880, immigration intensified. Economic development was already important and attracted many immigrants. Thus, more than 17 million new ones arrived, of which 15 million remained (11). These immigrants sought employment in the cities, where there was demand for industrialization, constituting more than a third of the workforce in cities with more than 100,000 inhabitants and 66% of the total urban population.
The same happened in the Ibero-American countries during the 19th century, although with a certain chronological delay with respect to what happened in the United States (12).
The strong rates of demographic growth experienced by the most dynamic cities in Europe and America are those that we find throughout our century in those of many countries on other continents.
In countries considered underdeveloped the evolution has been similar, although with much higher proportions and intensity during the 20th century (13). Over long periods, growths of up to 7, 8 and 10 percent can be detected, and this in both small and large cities.
The reasons for these growths have to do, on the one hand, with natural movement, which has become strong with the rapid decrease in mortality, keeping fertility high; and on the other, with the high immigration figures.