Prussia vs Preussen

Prussia and Preussen both are nouns.

Word	Noun	Adjective	Verb	Adverb
Prussia	Yes	No	No	No
Preussen	Yes	No	No	No

As nouns, Prussia and Preussen are synonyms defined as:

Prussia and Preussen: a former kingdom in north-central Europe including present-day northern Germany and northern Poland

Prussia (noun)	Preussen (noun)
a former kingdom in north-central Europe including present-day northern Germany and northern Poland	a former kingdom in north-central Europe including present-day northern Germany and northern Poland