While the initial evolution of the RPG from wargames involved an ever-tightening focus - moving away from the concerns of whole armies and towards the concerns of individuals, down to the contents of their canteens - eventually players of RPGs looked back up the scale of play and wanted to know how their actions effected and were informed by the worlds around them.
This concern about the organizations that surround PCs is the purview of realm management rules. Such rules can span a broad variety of scales and concerns. Realm management rules might address questions such as:
- How many members are in the PC's motorcycle gang?
- What did that goblin attack cost the duchy?
- Will that rival thief betray his guild or suffer in jail?
- Is there enough gold in the coffers to bribe that senator?
- Will the harvest bring enough or will there be famine?
- How many foot soldiers can I press into my service? How many armored cavalry?
Realm management also deals with tracking the internal and external pressures on a realm. Internal pressures might include the ambitions of a valued underling. External pressures might include the raids along your borders or the sudden influx of refugees from a war you're not involved in. Some realm management systems generate events like these.
They can also address violent conflicts between groups, but are not necessarily mass-combat or battle rules. Such rules are a subset of realm management.