The persecution of Jews in Germany and the Holocaust had several distinct effects upon psychology: a major geographical shift in the epicenter of the scientific psychology world, an influx of Jewish psychologists into American universities, and a major change in focus from behavior to social issues. Prior to that time, behaviorism dominated American psychology in both clinical and experimental subfields, and the influx of Jewish refugees into America had a pronounced effect upon research and practice.

Prior to 1933, Germany was arguably the center of the psychological world. The first scientific laboratory and academic department of psychology was founded in 1879 by Wilhelm Wundt at the University of Leipzig, and knowledge of German was considered essential for scientific literacy in the field, even in America. In advance of WWII, numerous psychologists fled Nazi Germany, with most settling in America. When Hitler rose to power in 1933, Jewish scientists were removed from academic posts. The most prestigious psychology post in Germany was held by Wolfgang Köhler, who was associated with the Gestalt school. Although not Jewish, he was a vocal opponent of Nazi ideology and wrote an article in 1933 that is considered to be the last published criticism allowed by the Nazi regime in Germany. After refusing to begin lectures with the Nazi salute, Nazi officials began harassing his students, leading him to resign. Köhler was also editor of the influential journal Psychologische Forschung (Psychological Research), which Hitler suspended. Köhler resumed editing it from Swarthmore College after emigrating to the U.S. in 1935.

Kurt Lewin was a Jewish psychologist associated with the Gestalt school in Germany. He was forced to leave the country in 1933 and turned his attention from perceptual phenomenon to studying the behavior of individuals in groups. He is widely considered to be the founder of the modern subfield of social psychology. According to Elliot Aronson, one of the main themes in post-war social psychology was to combat the idea that “crazy things are caused by crazy people.” The public largely believed that a flaw in the German character was responsible for the Holocaust, and it could not occur anywhere else. The 1950s and 1960s became one of the most productive periods in experimental psychology, as numerous researchers published studies that cast doubt upon the theory of the “Nazi mind.”

• Muzafer Sherif was a Turkish psychologist who was jailed for speaking out against the Nazi regime. The U.S. state department arranged for his release to America in 1944, where he conducted a series of experiments known as the Robber’s Cave studies that demonstrated that arbitrarily dividing people (in this case, children at a boy’s camp) into groups creates ingroup favoritism and outgroup derogation sufficient to lead to aggression.

• Soloman Asch was a Polish psychologist of Jewish descent who had immigrated to the U.S. in 1920. In the 1950s he published numerous influential studies of group conformity and propaganda.

• Stanley Milgram, a student of Asch, was an American born Jewish psychologist who was inspired by the trial of Adolf Eichmann to conduct a series of experiments on obedience to authority in the 1960s. His first published study demonstrated that the majority of people can be induced to administer lethal shocks to a complete stranger. This publication came out right as the war crimes trials shifted from the leaders to the low ranking individuals who carried out the actual killings, and had a significant impact upon the public interpretation of what had occurred.

• Leon Festinger, a student of Lewin, was an American born Jewish psychologist developed one of the most important theories of psychology, cognitive dissonance theory. The theory proposed that people experience physiological discomfort when they behave in ways that are inconsistent with their attitudes. In situations where they do not have complete control over their own behavior, they will avoid information that calls attention to this conflict and in some circumstances will revise their attitudes so that they are consistent with behavior.

• Stanley Schachter was an American born Jewish psychologist who developed a theory that emotions are comprised of two factors: nonspecific physiological arousal and a cognitive interpretation derived from environmental cues. Because the cognitive explanation for arousal is malleable, strong emotions can spill over very easily to each other: an experience of terror can directly lead to fanatical devotion, the exuberance of a rally can lead to aggressive hatred, etc.

The field of clinical psychology was also strongly shaped by refugees and Holocaust experiences. Psychoanalysis was almost entirely in the domain of Jewish central European psychiatrists (Carl Jung, a non-Jew, was the only notable exception). Refugees fleeing Germany gave psychoanalysis a much wider audience than it had received up until that point. Simultaneously, the U.S. military and Veterans’ Administration began to initiate psychologists in the practice of psychotherapy due to a shortage of psychiatrists, and many of these new entrants choose to practice using a psychoanalytic approach. Several new therapy approaches were also directly informed by Holocaust experiences. Viktor Frankl, an Austrian psychiatrist who survived imprisonment at Auschwitz and Dachau, noticed that a prime determinant of who survived and who died was the person’s sense of their life having meaning. He developed a new therapy approach, logotherapy, from these experiences.

I would highly recommend Richard Overy’s (2014) “Ordinary Men, Extraordinary Circumstances: Historians, Social Psychology, and the Holocaust” (Journal of Social Issues, 70, 515-530) and Robert Prince’s (2009) “Psychoanalysis Traumatized: The Legacy of the Holocaust” (The American Journal of Psychoanalysis, 69, 179-194) for further reading.

I can answer the philosophy side! Sorry if it's too late! I am a political philosopher so hopefully I can provide something up to standard. I will focus on western philosophy and more particularly France and Germany (I am less knowledgeable on the UK and the US but they also do a very different type of philosophy). Oh Boy. Holocaust and philosophy. I should start by saying that nothing could be done on the subject I think without 3 volume of 1000 pages each! It is astounding how philosophy was affected by the Holocaust and I will tell you why: Philosophy was going on with the assumption that NOTHING as bad as the Holocaust and more broadly World War II would ever occur. It is not that philosophers did not believe it would occur or not but instead that the intensity of the horror was never seen before and challenged many things that were discussed in philosophy up to this point. Everything that the Holocaust represents was a big middle finger to philosophy; particularly in three fields: philosophy of history, ethics, and political philosophy. It is a daunting task to really have an in-depth discussion on the topic through this medium but I will do my best and you can ask questions if you want more.

Philosophy of History: In the field of philosophy of history, a lot of what has been discussed so far has been teleogical. Coming first through Christianity and then through figures such as Kant, Hegel and Marx, history was seen as linear; as progressing. In the Christian sense, it would range from the birth of Christianity (return of Christ) to the Apocalypse and the Kingdom of God. In a Christian sense, it means that there are an Alpha and an Omega; a beginning and an end. Now, philosophers do not talk of the linearity of history in necessarily the same sense as an historian. Philosophers are interested in the perception of progress. Historians have to avoid discussing the linearity of history and make sure it does not taint their research but philosophically, the philosopher is not in a position in which he can ignore the appearance of progress. That things seem to somewhat become “better” to the uneducated man (as in anyone observing the world outside of his research mentality) needs to be addressed. So for Hegel, something such as war and peace, are two facets of society that in their seemingly conflictual relationship allow humans to achieve a greater understanding and attain Truth. Although I schematize Hegel dramatically here and oversimplify it, the idea is basically that history progresses through dialectical concepts allowing humanity to uncover its true rational nature. Most thinkers of the Enlightenment certainly had similar thoughts regarding the world and many argued that those philosophers simply “secularised” Christianity’s conception of history.

Marx is just as bad; although Hegel is an idealist, Marx is a materialist and will instead propose that the progression of history is material (who owns the means of production etc.) but once again, Marx is still in this conception of linear history. It is quite obvious in both Marx and Hegel in the way they address different time periods and how Marx thinks that were are slowly moving toward the final stage: communism.

Then comes WWII. How can you discuss a linearity of history; the world getting better when there is the Holocaust? It suddenly made no sense whatsoever. Even if humans discover their own selves as time goes by through their intellectual experiences, how can something such as the Holocaust be part of any linear conception of history? Although Marxism was still strong after WWII, it became glaringly obvious that there were issues with Hegelian philosophies. Although philosophers had pointed issues before, those issues were essentially philosophical in nature. The Holocaust was truly the horrible moment of human history that led to radical changes in how we perceived history from a philosophical point of view. This leads me to the second point: ethics and challenging the Enlightenment. For many philosophers, the Holocaust could only be explained by issues stemming from the Enlightenment. More specifically, religion and science.

In the case of religion, the argument is not that because there was no religion, people became Nazis and killed jews. More so that it allowed for a conception of the world in which the State is central to take place and to elevate the “body” to the level of religious. Nazi ideology put a strong emphasis on the body, appearance, being physically fit: in other words, making the object of worship something wordly; of this world. The violent rejection of religion while liberalism was weak (a lot of literature on the links between religion and liberalism but I don’t want to make this longer than it is already) allowed for a counterbalance in which the supremacy of the body took place; something we do not see in Christianity, Enlightenment ideals or Liberalism. This goes hand in hand with the will to permeate society with science. Nazi ideology of course placed a strong bond on making their ideas “scientific”. Careful here: many will point out Nazi rejected many sound science and the like but that is missing the point being made: that Nazis wanted a systemised construct of knowledge to found their principles. It is why they based so much of their ideas on bloodlines, artificial selection and the like. This led to philosophers such as Levinas to put forth ideas regarding a healthy relationship with the body. Liberalism, Christianity and the like focused too much on the mind at the expense of the body; the Nazis did it the other way around. For Levinas, the physical had to be reconciled with the mind and proposes an ethics based around the acceptation of the Other’s alterity when presented with the Other’s physical presence. Levinas was not just anyone: he was a Jewish philosopher who lost his family in the camps and was himself stuck in one for most of WWII. And many philosophers following WWII had to revisit philosophy as a field to account for the Holocaust. The intellectual roots of the Holocaust had to be studied and altered deeply the philosophical landscape.

Although Levinas is more in the field of metaethics, ethics as a field was of course affected. As discussed by my colleague who is a psychologist, many of the experiments and events during the Holocaust changed our perception of how much should we expect from society. Clearly, society did not revolt or defend people and experiments such as Milgram show that we must revisit the moral burden philosophical theories put upon people. Philosophers such as Kant would put a heavy burden on the moral agent and the Holocaust led ethicists to revisit the burden placed upon moral agents. On the utilitarian side, there was of course the obvious idea that clearly, the worst we fear from utilitarianism is not impossibility anymore. Humans could truly kill a staggering amount of people for the greater good. Although John Stuart Mill’s utilitarianism was more centered about what rules produce the greater good, the Holocaust showed that things could be fiddled with toward certain conception of the greater good and that clearly, ethics had to become a more practical field. And so, it did, gradually in philosophy departments, become a much more important part of ethicists. Last but not least: political philosophy. Political philosophy saw of course the rise of liberalism as something to be obvious. The horrific acts of the Holocaust and WWII more broadly moved fascism out of the way; anarchism was now also a lot less significant following defeats in Spain and Russia. Liberalism became opposed to Communism and so, the cold war begins. In that regard, the Holocaust made liberalism a pressing issue because for many, it demonstrated the necessity of many precepts put forth by liberal thinkers as to avoid a treatment of the minorities similar to the Holocaust. We did not exactly fear that the same thing would happen in the UK or Canada but more so that philosophically, it became obvious that a philosophical system like liberalism would avoid many pitfalls of fascism. WWII allowed also liberalism to take a solid hold following the defeat of Germany in intellectual communities with its only grand opponent being Marxism. I will stop for now but if you have any questions, I can certainly elaborate! It is a very complex topic and I am on a mobile. Also, English is not my first language! So I will review what I wrote a bit later since it is difficult to see if what I wrote is coherent while on a phone. Do not hesitate if you have any questions!