" 
 == Alternate hypotheses == 
 In the interest of fairness, let us consider all the hypotheses that could be put on the table.  For rhetorical reasons I'll temporarily lump nationality/ethnicity/language together. 
 * Copernicus was Dutch (or Belgian).  The Ostsiedlung involved many Dutch settlers coming to Prussia, and the Netherlands hosted many cities of the Hanseatic League. 
 * Copernicus was Swedish.  The Germanic peoples who displaced some Slavs from northern Poland a millennium and a half before his birth came from Sweden, and Sweden was important in the Hanseatic League too. 
 * Copernicus was Danish.  Or English.  (Hanseatic League trading partners, just for good measure) 
 * Copernicus was Lithuanian.  The King of Poland was the King of Lithuania, so he was a subject of the King of Lithuania. 
 * Copernicus was Roman.  As an ecclesiastic he was actually (I think) a subject of the temporal authority of the Roman Catholic Church, he spoke Roman, studied in Italy, lectured in Rome. 
 * Copernicus was German.  Many settlers in the Ostsiedlung came from Germany and Germany was one of the countries in the Hanseatic League, and it is true that the Duke of Prussia came from the Teutonic Order established by German conquest. 

 * Copernicus was Polish.  Copernicus was born in Poland, lived in Poland, was buried in Poland.  If you look at a map of Europe at the time when he lived and you want to find him, you look for the Vistula River in the middle of Poland.  He was a subject and advisor of the Polish king, and arranged the successful defense of Olsztyn Castle from an insurrection of the Teutonic Order leading to the Prussian Homage that reestablished the subordination of the Prussian duke to the Polish king.  If you would call him something other than Polish, well... take your pick.  "