Polish Citizenship

International law recognises territory.

Jus sanguinis – right of blood is an international principle that Poland adheres to, that means irrespective of place of birth your nationality is that of your Father.

The former Russian Empire that constitute parts of the Polish State is the recognised territory.

Therefore some categories who were denied nationality when the Republic of Poland was founded (Canadian and Americans specifically) can claim this nationality retrospectively by way of reinstatement / reclamation.