Is your score positive? You win! (Some players win more than others.)
A woman needs a man like a fish needs a saxophone.
Does this mean you can either remove a tribe or place a tribe?
My initial impression was the point of the ability was to "replace" enemies, but based on the above rule, it seems you can only add or remove an ally, not replace one.
In other words, are you replacing units with this ability? Or removing/adding units?
You get three remove/add actions, not three replace actions. For warbands, you can do one remove and one add for the equivalent of a replace. For allied tribes, it takes two separate Suborn actions to replace a tribe.