[inglor_cz]

The Commonwealth was an interesting entity.

Lithuanians were the last remaining pagans in Europe, retaining a lot of pagan customs and practices even after their nominal conversion to Christianity. Poles were much more devout Catholics.

The two languages are absolutely mutually incomprehensible, plus there were significant minorities that spoke other incomprehensible languages.

There wasn't any good road system etc., and the country had just a few ports worth their name. It also existed a dangerous neighbourhood: Prussia, Sweden, Turkey.

But it still endured for 400 years. That is quite remarkable. If I saw a Linux server with 25 years uptime, I would be equally surprised.