Nazi eugenics pertains to Nazi Germany's Nazism and race social policies that placed the improvement of the race through eugenics at the centre of their concerns and targeted those humans they identified as Life Unworthy of Life, including but not limited to: criminal, degenerate, dissident, feeble-minded, homosexual, idle, insane, religious and weak humans for elimination from the chain of heredity.
Hitler and eugenics
Hitler had read some racial-hygiene tracts during his period of imprisonment in Landsberg prison. The future leader considered that Germany could only become strong again if the state applied to German society the basic principles of racial hygiene and genetic engineering.
Hitler believed the nation had become weak, corrupted by the infusion of degenerate elements (similar to genes) into its bloodstream. These had to be removed as quickly as possible. The strong and the racially pure had to be encouraged to have more children, and the weak and the racially impure had to be neutralized by one means or another. Ironically, it has also been speculated Hitler had Parkinson's disease.
The Law for the Prevention of Hereditarily Diseased Offspring, proclaimed on July 14, 1933 required physicians to register every case of hereditary illness known to them, except in women over forty-five years of age. Physicians could be fined for failing to comply. In 1934 the first year of the Law's operation, nearly 4,000 people appealed against the decisions of sterilisation authorities, 3,559 of the appeals failed. By the end of the Nazi regime, over 200 "Genetic Health Courts" were created, and under their rulings over 400,000 people were sterilized against their will.
Sterilization to murder
Action T4 (German Aktion T4) was the official name of the Nazi Germany eugenics program which forcefully conducted euthanasia on Germans who were institutionalized or suffering from birth defects. In total, an estimated 200,000 people were killed as a result of the program.
The Hadamar Clinic was a mental hospital in the German town of Hadamar, which was used by the Nazis as the site of their T-4 Euthanasia Program.
Kaiser Wilhem Institute
The Kaiser Wilhelm Institute of Anthropology, Human Heredity, and Eugenics was founded in 1927. In its early years, and during the Nazi era, it was strongly associated with theories of eugenics and racial hygiene advocated by its leading theorists Fritz Lenz and Eugen Fischer, and by its director Otmar von Verschuer. Under Fischer, the sterilisation of so-called Rhineland Bastards was undertaken.
Applying racial hygiene
Applying the principles of racial hygiene to society meant sweeping away traditional morality and replacing it with a system of ethics that derived good and bad solely from the imagined collective interests of the master race.
Some physicians outside Germany also held the view that many social ills were the result of the hereditary degeneracy of certain sections of the population. Even before the Nazis came to power in Germany twenty-eight states in the United States had passed compulsory sterilisation laws resulting in the sterilization of 15,999 people; the total had more than doubled by 1939.  Over 60,000 people had been sterilized under U.S. compulsory sterilization laws before they became mostly unused in the 1960s. Many people were sterilized as children and did not know what had been done until they tried to conceive as adults.
Years and decades after the large-scale forced sterilization programs had ceased to exist in the US, many countries maintained post WWII sterilization campaigns lasting well into the 1970s.
In 1997 it was disclosed that Sweden in particular had a strong sterilization program, sterilizing around 62,000 individuals over a period of 40 years until 1976. In the United Kingdom, Home Secretary Winston Churchill introduced a bill that became the 1913 Mental Deficiency Act, which initially included a clause allowing forced sterilization of the mentally ill. Writer G.K. Chesterton led a successful effort to defeat that clause of the bill.
In 1990s Peru, the government of former president Alberto Fujimori was accused of having pressured 200,000 indigenous people in rural areas, mainly Quechuas and Aymaras, into being sterilized as part of a family planning policy. The Soviet Union imposed forced sterilization for female workers deported from Romania to Soviet labour camps, which occurred after World War II, when Romania was supposed to supply reconstruction workforce, according to the armistice convention.  India and China have at various times implemented sterilisation campaigns as a population control policy, although only the latter has made any previous overtures towards any potential eugenic motivations.
Other countries that had notably active sterilization programs include Australia, Canada, Estonia, Finland, Iceland, Norway, Panama, Slovakia and Switzerland.
The Roman Catholic Church has been a notable opponent of eugenics and sterilization programs since long before the creation of the Nazi state for religious reasons.
After revelations of the Holocaust and the connection between Nazi master race ideology and eugenics became well known, public support for eugenics became muted in the postwar years and eventually became non-existent, as eugenics became inextricably associated with the Nazi regime.
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