This is the 14810th most frequent German word.
preußischen
"Preußischen" means "Prussian" in English, relating to Prussia or its people, culture, or history.
'preußischen' is used as an adjective here, describing something related to Prussia, specifically 'Königsberg'. It is in its genitive case because it modifies a singular noun following 'im', which implies 'in dem' (in the).
Im preußischen Königsberg wurde einst Philosophie gelehrt.
Philosophy was once taught in Prussian Königsberg.
'preußischen' again serves as an adjective, describing 'Reformen' (reforms). It is in the nominative plural form, as it refers to something plural and works subjectively in the sentence.
Die preußischen Reformen im 19. Jahrhundert veränderten Europa nachhaltig.
The Prussian reforms in the 19th century sustainably changed Europe.
Here, 'preußischen' describes 'Königin' (queen) and is in the dative singular to match the indirect object 'der Königin'.