Neorealism (international relations)
Neorealism or structural realism is a theory of international relations first outlined by Kenneth Waltz in his 1979 book Theory of International Politics. Alongside neoliberalism, neorealism is one of the most influential contemporary approaches to international relations; the two perspectives have dominated international relations theory for the last decade. Neorealism emerged from the North American discipline of political science, and reformulates the classical realist tradition of E.H. Carr, Hans Morgenthau, and Reinhold Niebuhr. Realists in general argue that power is the most important factor in international relations.
Neorealism is an ideological departure from Hans Morgenthau's writing on classical realism. Classical realism originally explained the machinations of international politics as being based in human nature, and therefore subject to the ego and emotion of world leaders.  Neorealist thinkers instead propose that structural constraints—not strategy, egoism, or motivation—will determine behaviour in international relations.
Neorealism holds that the nature of the international structure is defined by its ordering principle, anarchy, and by the distribution of capabilities (measured by the number of great powers within the international system). 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 self-help, 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 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.
Within realist thought
While neorealists agree that the structure of the international relations is the primary impetus in seeking security, there is disagreement among neorealist scholars as to whether states merely aim to survive or whether states want to maximize their relative power. The former represents the ideas of Kenneth Waltz and defensive realism while the latter represents the ideas of John Mearsheimer and offensive realism.
With other schools of thought
Neorealists conclude that because war is an effect of the anarchic structure of the international system, it is likely to continue in the future. Indeed, neorealists often argue that the ordering principle of the international system has not fundamentally changed from the time of Thucydides to the advent of nuclear warfare. The view that long-lasting peace is not likely to be achieved is described by other theorists as a largely pessimistic view of international relations. One of the main challenges to neorealist theory is the democratic peace theory and supporting research such as the book Never at War. Neorealists answer this challenge by arguing that democratic peace theorists tend to pick and choose the definition of democracy to get the wanted empirical result[bias]. For example, the Germany of Kaiser Wilhelm II, the Dominican Republic of Juan Bosch, or the Chile of Salvador Allende are not considered to be "democracies of the right kind" or the conflicts do not qualify as wars according to these theorists. Furthermore they claim several wars between democratic states have been averted only by causes other than ones covered by democratic peace theory.
Advocates of democratic peace theory see the spreading of democracy as helping to mitigate the effects of anarchy. With enough democracies in the world, Bruce Russett thinks that it "may be possible in part to supersede the 'realist' principles (anarchy, the security dilemma of states) that have dominated practice ... since at least the seventeenth century." John Mueller believes that it is not the spreading of democracy but rather other conditions (e.g., power) that bring about democracy and peace. Confirming Mueller's argument, Kenneth Waltz notes that "some of the major democracies—Britain in the nineteenth century and the United States in the twentieth century—have been among the most powerful states of their eras."
- According to Sagan 2004, p. 91 n.4, Waltz's book remains "the seminal text of neorealism".
- Powell 1994, p. 313.
- Morgenthau, Hans J. Politics Among Nations: The Struggle for Power and Peace, 5th Edition, Revised. (New York: Alfred A. Knopf, 1978, p. 4-15)
- Waltz 1979, pp. 132–3.
- Waltz 1979, p. 133.
- Humphreys 2012.
- Mearsheimer 1995, p. 11 n.27, 16 n.27.
- Mearsheimer 2001.
- Waltz 2001, pp. 5–41.
- Waltz 2000, p. 4.
- Russett 1993, p. 24.
- Waltz 2000, p. 9.
- Humphreys, Adam R. C. (2012). "Another Waltz? Methodological Rhetoric and Practice in Theory of International Politics". International Relations 26 (4): 389–408.
- Mearsheimer, John J. (1994). "The False Promise of International Institutions". International Security 19 (3): 5–49.
- ——— (2001). The Tragedy of Great Power Politics. New York, NY: Norton. ISBN 0-393-02025-8.
- Powell, Robert (1994). "Anarchy in International Relations Theory: The Neorealist-Neoliberal Debate". International Organization 48 (2): 313–344.
- Russett, Bruce (1993). Grasping Democratic Peace. Princeton, NJ: Princeton University Press. ISBN 0-691-03346-3.
- Sagan, Scott (2004). "Realist Perspectives on Ethical Norms and Weapons of Mass Destruction". In Sohail Hashmi and Steven Lee, eds., Ethics and weapons of Mass Destruction: Religious and Secular Perspectives. New York, NY: Cambridge University Press. pp. 73–95. ISBN 978-0-521-83671-5.
- Waltz, Kenneth (1979). Theory of International Politics. Reading, MA: Addison-Wesley. ISBN 0-201-08349-3.
- ——— (2001). "Structural Realism after the Cold War". International Security 25 (1): 5–41. Retrieved 17 April 2013.