Which race would you add to Heroes?

The idea of a race that forces irreconcilable enemies to unite is intriguing. However, this would imply that this race is significantly more powerful than all others, which would create an imbalance. Therefore, this race shouldn't be too strong. What else could lead to all factions uniting against a single race? It could be a clash of ideologies. In this case, outcasts, with their ideology of equality and freedom, and amazons, with their ideology of matriarchy, would be a good fit.