In the late 1800s and early 1900s, American intellectuals and politicians, many of them political progressives, led an aggressive anti-immigration movement. Based on the pseudo-science of Eugenics, proponents argued that there was scientific proof of the inferiority of southern and eastern Europeans.
This lead to restrictive immigration laws that kept several generations of European immigrants out of the United States.
In his new book The Guarded Gate, Daniel Okrent delves into the history of the era of eugenics.
It's a story with significant relevance today.