I think I mentioned that I read a book about the atmosphere in Hitler's Prussia before WW II. Wankowicz, Polish journalist was able to visit some Polish as well as German settlements in Mazury region and Warmia in the time when this region was occupied by Germany. He saw Hitler's fervor and build in nationalistic feelings. He visited the remains of the Polish villages and people who were depraved of means to live if they wanted to declare their Polishness.... or try to send children to Polish school.
At least WW II changed it and after the war these regions became Polish again. It is a pity that Prussians were gone but at least Poles were here longer than German settlers and they are closer in culture and language to the original inhabitants.
I watched this video with mixed feelings. The person who does the video tried to be objective about the history but then he asked an expert who is defending Teutonic knights as like Prussians were the same guilty or even more. Still there is a lot of historical background there: