From Echoes of Angmar

Monster Tribes are the inverse of player Kinships. An orc fights best in a horde and players on the Creep side of the Moors conflict can join together to get the benefits of Kinships while fighting for the forces of evil. Monster tribes have tribal chat and the ability to have hundreds of members in a single tribe. Just like for player-created kinships, monster tribes will need a charter which is available for purchase at Gramsfoot. There must be six members to maintain the tribe and tribes are independent of any player's Kinship. You can only belong to one tribe at a time.