I like this.
Maybe the two factions that i made for Shneekeythelost's campaign setting would fit here. the gods are his makeing.

Let me show introduce you to:

The Yellow Warriors of the Mighty Sun
and
The Marine Combatents of the Watchful Moon

Spoiler
Show
Both factions are religously bound, as they belive that long ago Solomark the god of sun and honour sent his Greatest warrior, The Paladin, to fight Markaranak's Champion, the Hexblade (a better version of it).
The Paladin killed the Hexblade, but died from the poison the HexBlade used.

So the YWotMS built their castle where the clerics ''throw a flower up the air and wher they fly is the diraction of the sword because flowers mourn the Paladin'' technique led them, and the MCotWM built their castle* using the smae technique about a day of ride distance from the YWotMS castle unknowingly.

So they fight for many reasaons:
1) Since the Paladin and the HexBlade died near each other, they fight about the location of the swords
2)They are moral enemies: Honor vs. Deception.
3)The yellow warriors use fire, while the marine combatents use ice.
4)Dignity- they will never forgive the other for killing their champion.
5)The large similarity: "you stole our idea!" "no you stole ours!"

*Barely a castle, more like a large stone house with court, blacksmith, stables, shrine, barracks and some farms, surrounded with a small wooden palisade with battlements and a few towers.

Among the factions there are minor orders:
The yellow warriors have:
The Golden order:Brave and manly Paladins.
The Rays of Solomark: Clerics of holy stuff.
The Blazes of his rage: Wizards specilaizeing in fire

The leaders of each order compete and the winner is the Grandmaster of the yellow warriors, the advisor of the King: THe descendent of the Paladin

The marine combatents have:

The blades of the moon:Hexblade order with no codes of honor.
The light of Markaranak: Peacefull clerics
The night freezers: Wizards of Ice.

They have a King who is the descendant of the HexBlade and the three leaders of the orders manage diffrent aspects whithin the kingdom.

each side has villages loyal to it, and they provide food and soliders for the endless battles with the enemy.

A Solomark Paladin is a lawfull barbarian. nothing more.
a Markaranak HexBlade is a hexblade wearing medium armor and uses posion and dirty tricks.


The lands between the two factions are filled with either monsters eating corpses or Armies fighting. Armor and weapons may be looted from the corpses without need to worry about the monsters, as they will be gratefull when you take the non-food off the food.