https://encyclopedia.ushmm.org/content/en/article/victims-of-the-nazi-era-nazi-racial-ideology
https://en.wikipedia.org/wiki/Anti-Slavic_sentiment
"Though anti-Slavic sentiments reached their peak during Nazi Germany, Germany has had a long history of Slavophobia. In particular, the Germanic people of Prussia often depicted Polish people in a negative light, which paralleled future Slavophobia in the Nazi regime. The Teutonic Order played a foundational role in shaping early German anti-Slavic sentiment through its participation in the Drang nach Osten ("Drive to the East"), a medieval and later nationalistic concept referring to German expansion into Slavic and Baltic lands. Beginning in the 13th century, the order launched crusades against pagan and Slavic populations in the eastern Baltic region, including Prussians, Lithuanians, and Pomeranians, under the pretext of Christianization and a civilizing mission. The conquest and colonization of these territories involved the suppression of native Slavic and Baltic cultures, forced conversions, and the settlement of German colonists. These actions were justified by portraying Slavic peoples as barbaric, morally deficient, and politically inferior, a narrative reinforced by Teutonic chroniclers such as Peter of Dusburg. The order imposed German legal systems and language, contributing to a lasting cultural hierarchy in which German identity was seen as superior." (and it is)
