And, obviusly... What would be the POD able to take Russia, Prussia and Austria out Poland? Experts on Polish History, you are welcome!
In my project
https://www.alternatehistory.com/discussion/showthread.php?t=36940 Russia is taken out because there was no unification of Russia in the first place (Poland offered it’s support to Novgorod (this is the POD) and Ivan III died in battle before marrying Sophia), Prussia will be taken out because it will be reintegrated into the Commonwealth (polish politics paying more attention to the north and king not allowing the other branch of Hohenzoller to inherit) and Austria will stay (thought probably small buffer state of Hungary will stay as well)
Problems:
Poland's weak internal structure (aristocratic democracy in a age of increasing absolutism).
Very difficult one. In my project there would be three main ways to achieve that:
-Successful reformation (this will hopefully lead to growing importance of cities and the middle class, as well a pursuing a more “capitalist” economy instead of feudal)
-Sneaky laws ensuring that there is no legislation paralyze if Sejm failed to reach a conclusion . (It’s too late to not let Nihil Novi
http://en.wikipedia.org/wiki/Nihil_novi happen, but what if it was later modified in a way that says: “If Sejm was concluded without making any decisions, than Senate may make any decisions as if they were made by Sejm.* If Senate had not make any decisions, than King may make any decisions as if they were made by Sejm.”**)
*This line is for magnates, without it noone is going to support this law during voting in Sejm.
**So, if we have a weak and divided Sejm and sneaky and strong enough to disrupt the work of the Senate and afterwards introduce same laws that would strengthen his position. The King will inevitably face a civil war, but he might win it if he has:
-An army loyal to the king (Probably raised with the help of increased taxes and revenue from cities. You would also need a reason to keep such an army. Cossacks-Hungarians-Russians-Ottomans alliance partitioning Ukraine seems a good one.)
There is also the fact that at the end of XV and beginning of XVI century (only decades after the POD) polish nobles are not yet “corrupted” and many of them care for the country and have a healthy look a the politics.
Poland's restive south (Cossack Ukraine).
Difficult one as the main possessions of polish magnates lie in the south, so it is unlikely to just abond them. There is a lot of empty land there, just waiting for proper colonization (main reason Poland did not have oversea colonies).
Give Ukraine to the Russians?
Not without a fight I afraid – but in the end I think it would be better for them to have it. (and fight for it with ottomans and Hungarians.)
The increasing strength of her neighbours (Prussia, Austria, Russia).
Explained above.