Emil Kraepelin was a physician who studied people with mental illness in the late nineteenth and early twentieth centuries in modern-day Germany. Kraepelin's examination and description of the symptoms and outcomes of mental illness formed the basis for his classification of psychiatric disorders into two main groups, dementia praecox, now called schizophrenia, and manic-depressive psychosis, now called bipolar disorder. He was one of the first physicians to suggest that those researching mental illness should gain scientific knowledge only through close observation and description. However, Kraepelin also believed that genetics played a role in the development and course of mental illness and characterized mentally ill people as weak-willed, which some have argued contributed to stigma about mental illnesses that persist today. Although some historians have pointed out issues with Kraepelin’s teachings, Kraepelin helped to establish psychiatry as a clinical science, which prompted future experimental investigations into mental illness.

In 1917 the Oregon State Legislature, in Salem, Oregon, passed a bill titled, 'To Prevent Procreation of Certain Classes in Oregon.' Passage of the bill created the Oregon State Board of Eugenics, an organization that presided over the forced sterilization of more than 2,600 Oregon residents from 1917 to 1981. In 1983, Legislation abolished the State Board of Eugenics, by that time called the Oregon State Board of Social Protection. For more than seventy years, the State Board was involved in the US eugenics movement, using theories partly constructed from genetics to control the reproductive health of citizens.