History /
History of Poland in a pill - illustrated [41]
Greeks and Romans had also slaves and It doesn't mean that their nation was not existing.
But slaves weren`t considered nation. The same with Poland - only royals and nobility were nation for a long time here.
Nation may refer to a community of people who share a common language, culture, ethnicity, descent, or history.
Tell it to the Polish magnates and szlachta a few hundred years ago. :):) I assure you they wouldn't be so enthusiastic about it. You might end up fighting a duel with an annoyed noble.
2. Kings and queens
Casimir the Great
found a Poland made of wood and left it made of stone". in 14 century. Considered one of the greatest kings of Poland.

Till today we can see his production:

etc etc
2. Kings and queens
1525, Polish king Sigismund Old receives homage from the Prussian prince:

en.wikipedia.org/wiki/Prussian_Homage
This plaque in Krakow`s Market Square reminds of the event

Sigismund Old`s son, Sigisimund August, fell in love and married a woman against his mother`s and ruling class members` wish, causing a great scandal.
en.wikipedia.org/wiki/Barbara_Radziwi%C5%82%C5%82
The young wife was allegedly poisoned and the king never got over her death.

See their story in a nice 1980s Polish film trailer:
youtu.be/o_H3jU4Qwbk