Quote Originally Posted by therother
The data text files have been released: https://forums.totalwar.org/vb/showthread.php?t=73971. The descr_faction_standing.txt file reveals quite a bit about what affects your relations with the Pope, as well as other factions, and your global reputation. Worth a read IMO.
Note the part where the faction standing is normalised downwards each turn for both Hard and Very Hard dificulties (with it just occurring faster on Very Hard).

Also note the "Tall Poppy" functionality where the top scoring factions (if significantly larger) automatically become more unpopular with every turn.

Note also there appear to be many more ways to score negative relationship points than there are positive (true to life as any married man can tell you... )...

So if you want a game where the cards are not unfairly stacked against the player then you need a Medium campaign difficulty.

It will be interesting to go through the other campaign AI files to see what else changes with difficulty...