The anti-immigration wave that has emerged over the last years on both sides of the Atlantic has contributed to spreading a number of mantras about the migration phenomenon on a global scale. I myself have tried to debunk some of the myths related to the economic impact of immigrants on host countries, pointing out that most claims are either false or overstated (e.g., here, here, or here).
However, most people aren’t so worried about the long-term economic effects of immigration, which, after all, are difficult to assess for non-economists. They are more concerned about the potential threat that a massive increase in the immigrant population would pose to developed countries. That’s why anti-immigration populists like Trump or Salvini have focused on raising the specter of an alleged invasion that needs to be halted.
The problem with the invasion rhetoric is that it’s at odds with the facts. We just need to look at the latest Trends in International Migrant Stock report developed by the Population Division of United Nations to verify this. Rather than analyze migration flows, this report focuses on the number of migrants living in a particular country, which gives a more accurate view of long-term migration trends. It should be noted the following numbers largely rely on official statistics from national censuses, which often include both regular and irregular migrants. This guarantees that at least a fraction of the undocumented migrants are included in the estimates.
In 2017, the number of international migrants (i.e., people living in a country other than their country of birth or citizenship) was 258 million. Even though the number has increased considerably since 1970, it only represents a 3.4 percent of the world population, or 1 out of 30 world citizens.
Contrary to what it may seem, only a little more than half of all international migrants live in developed regions (i.e., Europe, Northern America, Australia, New Zealand and Japan), of which European countries host around 78 million and the US, 50 million. In relative terms, however, these numbers are low when compared to their populations, representing 10 and 15 percent respectively. For its part, Asia hosts 79 million, that is, 31 percent of the total number of international migrants.
The main concern of most anti-immigration advocates isn’t immigration per se (or so they claim), but irregular immigration. Since irregular immigration is more often than not low-skilled, we can check which fraction of the migrant stock in European countries come from low-income (mainly sub-Saharan countries) and lower-middle income countries. Interestingly, the number is relatively low: only 28,7 percent of all migrants living in Europe come from the poorer countries. This is in line with the fact that 70 percent of sub-Saharan migrants move within the African continent.
The above numbers don’t fit with the rhetoric of an alleged invasion, confirming that migration restrictions work. Yet this isn’t good news. The economic cost of barriers to migration amounts to $1 trillion as suggested by a paper published a few years ago. In other words, if we eliminated or even partially reduced migration barriers, the economic gains would be huge. What are we waiting for?
 According to UN’s Recommendations on Statistics of International Migration, “census data have provided the data for the most comprehensive set of estimates of the total migrant stock in countries in the world.”
 The total number of international migrants living in Europe includes those Europeans that live in a European country other than their country of birth or citizenship.