“If rich countries were to admit enough migrants from poor countries to expand their own labour forces by a mere 3%, the world would be richer, according to one estimate, by $356 billion a year. Completely opening borders would add an astonishing $39 trillion over 25 years to the global economy. That is more than 500 times the amount the rich world spends on foreign aid each year. Migration is the most effective tool yet devised for reducing global poverty.”