 2.5 million ethnic Poles, 0.5 million ethnic Serbs and 0.22–0.5 million Romani were killed by the regime and its collaborators.The Nazis considered most Slavs to be non-Aryan "Untermenschen".The Nazi Party's chief racial theorist, Alfred Rosenberg, adopted the term from Klansman Lothrop Stoddard's 1922 book "The Revolt Against Civilization