Structural realism holds that the nature of the international structure is defined by its ordering principle (anarchy), units of the system (states), and by the distribution of capabilities (measured by the number of
great powers within the international system), with only the last being considered an
independent variable with any meaningful change over time. The anarchic ordering principle of the international structure is
decentralized, meaning there is no formal central
authority; every sovereign state is formally equal in this system. These states act according to the logic of
egoism, meaning states seek their own interest and will not subordinate their interest to the interests of other states. States are assumed at a minimum to want to ensure their own survival as this is a prerequisite to pursue other goals. This lack of trust, based on uncertainty, is called the
security dilemma. Neorealism sees states as
black boxes, as the structure of the international system is emphasized rather than the units and their unique characteristics within it as being causal. 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. Neorealists argue that processes of emulation and competition lead states to behave in the aforementioned ways. Emulation leads states to adopt the behaviors of successful states (for example, those victorious in war), whereas competition leads states to vigilantly ensure their security and survival through the best means possible. Due to the anarchic nature of the international system and the inability of states to rely on other states or organizations, states have to engage in "
self-help." This is in contrast to some classical realists which did see norms as potentially important. Neorealists are also skeptical of the ability of international organizations to act independently in the international system and facilitate cooperation between states. A foundational study in the area of defensive realism is
Robert Jervis' classic 1978 article on the "security dilemma." It examines how uncertainty and the offense-defense balance may heighten or soften the security dilemma. Building on Jervis,
Stephen Van Evera explores the causes of war from a defensive realist perspective.
Offensive realism Offensive realism, developed by Mearsheimer differs in the amount of power that states desire. Mearsheimer proposes that states maximize relative power ultimately aiming for regional hegemony. Eric Labs investigates the expansion of war aims during wartime as an example of offensive behavior.
Fareed Zakaria analyzes the history of
US foreign relations from 1865 to 1914 and asserts that foreign interventions during this period were not motivated by worries about external threats but by a desire to expand US influence. ==Scholarly debate==