The setting : a world at a nexus of realities called the Axis. It's a place where different aspect of reality collide. Elements, though, lights, concepts, shapes... Each of those has its own world close to the Axis. Anyone can use those primal forces as magic and even travel to the various worlds. On the other hand, the more you are attuned to one reality, the harder it is to contact the others, up to the point where one become one with its preferred reality. Those who get this far are called Sources as the act like a source of their preferred reality. They are really powerful, free from most limit of the Axis "rules" as long as they act within their own reality rules.
The Axis inhabitant are mainly linked to elemental planes and a transcending though-plane. The lords of those two realities have a kind of higher authority over the other, being each at the end of the spectrum of realities.
While everyone on the axis perform some magic to help with every day tasks, those that make that their job are called mages.
The main continent is shaped like a croissant, with the opening at the north. The west side is primarily occupied by people tied to the elemental lords.
On the equator, there is a huge Forest called "Maiden Forest" heavily link to Earth and Wind elements, with pocket of anything fluctuating around.
Below, there is a land shattered by too many realities interacting. The lord of this land is called Gorthor's the immortal.
This guy is your regular villain : powerful himself, with cunning, scheming and powerful mage underling, lots of soldiers,...
His realm maintain a low level state of war with his neighbours as the underlings try to bring more gifts and power to their master.
All he cares for is power and his own pleasure (have I said he is a big bad guy ?). His goal is to become a Source of several realities. So far he has managed to be a Source of elemental power and use other realities magic. This is a huge accomplishment, but he needs more guinea pigs.
The population has to cope with reality shift regularly as Gorthor's Lieutenant fight and scheme against one other. One day they live by a lake created by a water mage, the next they have to cope with a fire forest (not, not a forest on fire) sent by his fiery concurrent, then they are in 2D because a Shape Source has decided to take control of the region. Inhabitants are also drafted into the army and taken as guinea pig for the various mages experiments. As long as his realm does not collapse, Gorthor does not care.
So, how does Gorthor's domain not collapse?
Why don't people just revolt and throw him out of power.
I'm not asking for a realistic explanation, as the setting is high fantasy. I'm waiting for believable, logic and explainable, within the setting defined. Details can be handwaved but the broad picture has to make sense.
I have more detailed explanation and some reasons for this kingdom to keep on going but I think that giving away more would just limit creativity.