Nazi eugenics
The eugenics movement was very popular in the United States by the time it spread to Germany. California eugenicists began writing things that encouraged eugenics and sterilization, and sent them to German scientists and medical professionals. By 1933, California had forced more people to get sterilized than all of the other U.S. states combined. The Nazis got the idea for their compulsory (forced) sterilization program partly from California's program.