Harden your hearts.
According to the Office of the UN High Commissioner for Refugees, 68 million people around the world are or at risk of becoming refugees. The migration of a few million people has already turned the European Union inside out and motivated the election of an America-first presidency. What we have seen so far, though, is nothing compared to what is to come.
Fertility is declining in almost all the educated and prosperous parts of the world, notably including East Asia. But it remains extremely high in the least-educated parts of the world with the worst governance and the poorest growth prospects.
At constant fertility, the number of people aged 20 to 30 years will grow from 1.2 billion to almost 4 billion over the present century, and all of the growth will occur in Africa and South Asia (notably in Pakistan, where total fertility is 3.6 children per woman vs. 2.4 in India). Africa will be the main source of new young people.