Why does "Divine Mandate" give Slavery Tolerance? What if you don't want you're Divine Mandate nation to be pro slavery and the religion to be anti-Slavery?
Divine Mandate governments grant bonuses to the population's willingness to accept conditions of extreme hardship- both slavery and war- presumably because they're based on advancing the principle of religiously-fueled obedience to the ruler. An anti-slavery theocratic government would be done better as a Theocratic Oligarchy; a somewhat more moderate monarchy with elements of the 'divine right to rule' could be done as a Despotic Empire (which, despite the bonuses to work slaves harder, still has a valuable reduction to building costs). The HRE in general definitely had serfdom for much of its history, which would be a form of slavery.
I think the key thing about Fanatic Spiritualism is not that that physical reality is an
illusion, but rather that it's fundamentally
subordinate to supernatural reality, which would be consistent with a medieval Christian worldview. Fanatic Spiritualists don't have to reject research into physics and engineering, after all! What they
would reject is the idea that understanding of the physical world is the only thing to pursue. They would hold that a study of physical phenomena that rejects the role of the divine or supernatural is fundamentally incomplete.
