Man has always migrated. The mobility of the species has gradually populated our planet, with humans now spread across the globe. Traditionally, up until the first half of the 20th century, migration flows went south to north. However, since 1950 these movements have been somewhat reversed. Demographers draw a distinction between a foreigner – a notion that takes into account nationality – and an immigrant – a notion that refers to the country of birth.
It is now estimated that there are 200 million immigrants around the world, just 3% of all human beings. Some leave their country to rejoin their families, others migrate for economic reasons, while many escape their homeland as refugees. Analysing international migration is a good way of assessing the health of societies and their prospects for the future.