Here's some suggestions:
Monotheism All divine powers come from a single god. Other gods are worshipped, but they don't exist and don't grant powers. Characters with divine power can't fight each other.

Civilisation All the productive parts of the world are under the control of a handful of large, highly organised states. There are wildernesses and lawless areas, but only in very unproductive areas like the interior of jungles, deserts, and tundra. Of course there's plenty of crime and intrigue inside the states.

Monsters are rare. The civilisations have tried very hard to exterminate monsters within their territory, and mostly succeeded.

Behaviour matters. Several classes require codes of behaviour from the characters. Violation of the codes stops the class powers from working, either temporarily or permanently.