Donald J. Trump’s promise to build a wall to keep Mexicans and Central Americans from crossing the United States’ southern border was central to his successful campaign for the presidency. Antipathy toward immigrants is spreading through Europe, fueling Britons’ desire to leave the European Union, upending Italy’s political establishment and giving the populist Hungarian government of Viktor Orban a fourth term.
Fear of immigrants takes different forms. Immigration from the Middle East and North Africa has led to calls in Europe to prevent its so-called Islamization. In the United States, despite a long history of cultural, religious and ethnic mixing, several studies have concluded that alongside their anger over lost jobs and stagnant wages, many of the non-Hispanic white voters who tipped the presidency to Mr. Trump were motivated by fears that they were losing demographic ground to other groups.