Ezra Klein:

“According to Massey, the rise of America’s large undocumented population is a direct result of the militarization of the border. While undocumented workers once traveled back and forth from Mexico with relative ease, after the border was garrisoned, immigrants from Mexico crossed the border and stayed.

‘Migrants quite rationally responded to the increased costs and risks by minimizing the number of times they crossed the border,’ Massey wrote in his 2007paper‘Understanding America’...