The Economist | A world of walls https://www.economist.com/special-report/2019/11/16/to-make-the-world-richer-let-people-move?frsc=dg%7Ce
If everyone who wanted to migrate were able to do so, global gdp would double, estimates Michael Clemens of the Centre for Global Development, author of a forthcoming book, “The Walls of Nations”. No other policy change comes close to generating such colossal rewards. If there is $90 trillion a year up for grabs, you might think that policymakers would be feverishly devising ways to get a piece of it. They are not.