Waltz argues that the world exists in a state of perpetual international anarchy. Waltz distinguishes the anarchy of the international environment from the order of the domestic one. In the domestic realm, all actors may appeal to, and be compelled by, a central authority - 'the state' or 'the government' - but in the international realm, no such source of order exists. The anarchy of international politics – its lack of a central enforcer – means that states must act in a way that ensures their security above all, or else risk falling behind. This is a fundamental fact of political life faced by democracies and dictatorships alike: except in rare cases, they cannot count on the good will of others to help them, so they must always be ready to fend for themselves.
Like most neorealists Waltz accepts that globalization is posing new challenges to states, but he does not believe states are being replaced, because no other non-state actor can equal the capabilities of the state. Waltz has suggested that globalization is a fad of the 1990s and if anything the role of the state has expanded its functions in response to global transformations.
Neorealism was Waltz's response to what he saw as the deficiencies of classical realism. Although the terms are sometimes used interchangeably, neorealism and realism share a number of fundamental differences. The main distinction between the two theories is that classical realism puts human nature, or the urge to dominate, at the center of its explanation for war, while neorealism stakes no claim on human nature and argues instead that the pressures of anarchy shape outcomes regardless of human nature or domestic regimes.
Waltz's theory, as he explicitly makes clear in "Theory of International Politics", is not a theory of foreign policy and does not attempt to predict or explain specific state actions, such as the collapse of the Soviet Union. The theory explains only general principles of behavior that govern relations between states in an anarchic international system, rather than specific actions. These recurring principles of behavior include balancing against threats, entering into individually sub-optimal arms races, and exercising restraint in proportion to relative power. In Theory of International Politics (1979:6) Waltz suggests that explanation rather than prediction is expected from a good social science theory, since social scientists cannot run controlled experiments that give the natural sciences so much predictive power.
Since its appearance in 1979 and until the end of the Cold War neorealism was the dominant theory of international relations. Its inability to explain the sudden and peaceful collapse of the Soviet Union put into question Waltz's argument that bipolar systems should be more stable than multipolar systems. Waltz has argued that stability has been misunderstood to mean duration rather than peace, and that the bipolar system was indeed more stable in the latter sense.
Another major criticism of neorealism (and classical realism in general) is its inability to account for lasting great-power peace since World War II and increasing cooperation among states. Alternative explanations that focus on the roles of institutions, norms, and domestic regimes have become much more prominent, although realist theories continue to have a major influence on current work and theory.
Other critics have argued that states do not engage in balancing behavior as neorealism predicts, and instead often prefer to bandwagon, or side with the more powerful side in an international crisis. Waltz responds that his theory explains the actions of middle and great powers, and that small vulnerable states indeed often bandwagon instead of balance, but that ultimately their actions do not shape the course of international relations to a significant extent.
In Man, the State, and War, Waltz proposes a three-images view of looking at international relations behavior. The first image was the individual and human nature; the second image the nation-state, and the third image the international system.
In Theory of International Politics, Waltz elaborates many of the core principles of neorealist international relations theory, adopting a structural perspective that sets him apart from earlier (classical) realists like E.H. Carr and Hans Morgenthau, and later giving rise to the Neoclassical realist movement (Randall Schweller, Jack Snyder, Thomas J. Christensen, etc.) which tries to incorporate a structural component while emphasizing the state-society relationship that mitigates structural forces. (This book also popularized the term bandwagoning.)
In The Spread of Nuclear Weapons: A Debate Renewed, Waltz argues for the virtues of a world with more nuclear weapon states because of their power in nuclear deterrence. Sagan argued against the proliferation of nuclear weapons. See nuclear peace.