Neorealists contend that there are essentially three possible systems according to changes in the distribution of capabilities, defined by the number of great powers within the international system. A unipolar system contains only one great power, a bipolar system contains two great powers, and a multipolar system contains more than two great powers. Neorealists conclude that a bipolar system is more stable (less prone to great power war and systemic change) than a multipolar system because balancing can only occur through internal balancing as there are no extra great powers with which to form alliances. Because there is only internal balancing in a bipolar system, rather than external balancing, there is less opportunity for miscalculations and therefore less chance of great power war. That is a simplification and a theoretical ideal.