It’s simple: if your boss can hire someone else for cheaper, or threaten to, you have less leverage for bargaining. In the nineteenth century, employers’ ability to pay black workers a fraction of white wages made whites see free black people as threats to their livelihood. In the early twentieth century, new immigrants were added to this competitive dynamic, and the result was a zero sum: the boss made more profit; one group had new, worse work, and the other had none.
