Every Unit in the game is a member of a Tribe. There are 4 Tribes in the game.
Each tribe has a counter that is recommended within the game. The pattern for this is as follows:
Orc > Human > Elf > Undead > Orc
Senior units within a tribe gain an additional immunity to a specific crowd control mechanic depending on ther tribe.
Each race has an associated secret skill which can be unlocked and upgraded for gems in the Shop->Premium tab of the game. At the base level the skill requires members of the Tribe in the active team to work, at the top level this requirement is unneeded. The 4 kills are: