UPDATE 1.2 OF REDDIT CONTROLS EUROPE: RELIGIONS

your country can now adopt a state religion, although its not strictly necessary. if given, your country will be an ecclesiastic one of course. if not, your country will simply be secular. you can also choose to impose state atheism.

PS: some ideologies don't go well with religions! for example a communist state cant impose forced state religion, although it can be secular.

furthermore, this also adds crusades, where countries of the same religion (or branch of religion, like catholicism) can align to attack another country with another religion all at once, which is definitely costly but also very devastating