States are assumed at a minimum to want to ensure their own survival as this is a prerequisite to pursue other goals. This driving force of survival is the primary factor influencing their behavior and in turn ensures states develop offensive military capabilities for foreign interventionism and as a means to increase their relative power. Because states can never be certain of other states' future intentions, there is a lack of trust between states which requires them to be on guard against relative losses of power which could enable other states to threaten their survival. This lack of trust, based on uncertainty, is called the security dilemma.
States are deemed similar in terms of needs but not in capabilities for achieving them. The positional placement of states in terms of abilities determines the distribution of capabilities. The structural distribution of capabilities then limits cooperation among states through fears of relative gains made by other states, and the possibility of dependence on other states. The desire and relative abilities of each state to maximize relative power constrain each other, resulting in a 'balance of power', which shapes international relations. It also gives rise to the 'security dilemma' that all nations face. There are two ways in which states balance power: internal balancing and external balancing. Internal balancing occurs as states grow their own capabilities by increasing economic growth and/or increasing military spending. External balancing occurs as states enter into alliances to check the power of more powerful states or alliances.
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.