I am hoping someone can point me to a relevant thread, or can advise me from personal experience:
I have noted that factions will no longer give you money to attack other factions once you have taken aggressive action against them (the faction you are asking money from, not the one you have promised to attack), or have taken one of their cities by any means. I have fallen ill of factions whom I have not offended in those ways, however, and am uncertain of how exactly the relationship is spoiled.
Predictably, how quickly the relationship sours has nothing to do with whether or not the faction is allied, neutral, or even at war with you.
The relevant factors seem to be at least one of the following:
a. How much you get from the opposing faction, in an absolute sense; i.e., cp faction X is assigned 10,000 units to grant the player faction(s) for attacking other factions for the duration of the game.
3. How many times the faction is asked to contribute financially to your military efforts; i.e., cp faction Y is permitted 13 Diplomacy actions of type x with player faction(s) before refusing to make further donations.
VI. How many turns they have been asked to contribute to one's military campaigns; i.e., cp faction Q can perform diplomacy action z, any number of times, for up to 5 turns before refusing further diplomacy.
Perhaps some further variations are possible. Feel free to speculate. Concrete insight would be most appreciated as I like to take money from Peter to fight Paul, and I am eager to optimise my efforts.