An Orc's tribe influences his approach to combat and his abilities.
The tribe of a region's Overlord influences the entire region, affecting ambient activities and providing you with unique opportunities. For example, the Marauder tribe loves treasure, so when they control a region, you can find Mirian chests to loot. The Feral tribe focuses on hunting, killing, and controlling Beasts, so drake bait is plentiful in regions they control.
When you conquer a region, you install your own Overlord to command the fortress. His tribe determines which bonuses the region provides you.
The following is a list of the 7 tribes in the game Middle-earth: Shadow of War.