While anti-semitism has had a long history in Europe, Slavophobia and the view that they are subhuman and should be exterminated seemingly came out of nowhere pre WW2. Was there such extreme anti-Slavic racism among the populace before Hitler's time or did he and the Nazis just kind of invented it themselves and everyone just went with it?
/u/commiespaceinvader has previously answered What was Hitler's position on the Slavic people?
EDIT: See also Why is the Generalplan Ost considered different from the Holocaust? feat. /u/gingeryid alongside commiespaceinvader.