Speaking of religion, there should be more resistance to conversion. in EU3 its very easy to convert a large number of provinces into your religion in a relatively small period of time which is rather unrealistic.... Poland-Lithuania's demise was largely caused by its attempt to force catholicism on the Cossacks, they made a huge rebellion and they were joined by Russia. Religion-driven friendships and enemities as well as alliances do exist in EU3 but it doesnt really serve the purpose it served in history, which was to protect religious minorities that follow the alliance's beliefs, what happens in EU3 is mostly conquest
Not true. Missionaires uppers the revolt risk, and may triger the zealots uprising.
And it is not true, the Cossak-Poland war, was much more about culture and abolishment of serfdom(via getting independance, in a serfdom-free state). Zaporozhye was never a subjet of Poland. In a sence, it was a Zaporozhye- Crimean attack on the Poland-Lituinia, that got wast support among the Poland-held territories populated by Ukrainians, and the Cossacs that were on Polish service.
The attack won the consession, but then, peace expired and P-L reconquested part of the land.
Oh, and Cossaks didn`t quite joined Russia, they were firs allies, and then gradually become less and less independent, to the point where Russia basically diploanexed them.
In the initial years of alliance, there was no intend to join Russia.
Although, it would be great if the same culture and religion population of enemy country could revolt to help you fight.