Idealism vs. Realism: The Founding Debate in International Relations Theory

Nearly every later school of thought in international relations theory ultimately traces back to one founding argument: whether states can be trusted to behave morally, or whether they can only ever be relied upon to pursue their own power. That argument has a name – idealism versus realism – and it’s the debate that turned international relations from a loose collection of observations into a genuine field of theory.

Idealism: Law and Morality Over Force

Idealism is the older of the two schools, and its founders shared a common conviction: that international law and international institutions, properly built and properly supported, could resolve disputes between states without resorting to war. Idealists never claimed war was impossible – they treated it as a genuine curse on humanity – but they refused to accept that it was inevitable. Their central argument was that war persists mainly because the world hasn’t yet built international institutions strong and legitimate enough to replace it; get that right, and humanity could largely escape war’s grip. The tradition drew support from figures as varied as Woodrow Wilson, Bertrand Russell, and Mahatma Gandhi, each contributing to the case that ethics, not force, should be the organizing principle of relations between states.

Idealists rejected the idea that raw power politics is simply how governments must operate. Good governance, in their view, comes from good conduct, not from the accumulation of force. States, they argued, are not fixed in their behavior – a country’s foreign or domestic conduct shifts according to the moral or immoral goals it pursues at a given moment, which means a state can, with the right effort, learn to control and improve its own behavior over time. Several ideas run through idealist thought consistently: that international relations shouldn’t be studied only through the history of political and legal institutions, but through attention to individuals, since the problems facing people and the problems facing states are not fundamentally different; that human nature is not fixed for all time but capable of genuine moral improvement through sustained effort; that a state should only pursue agreements that actually benefit the people they’re meant to serve, rather than actions that risk catastrophe for humanity as a whole; and that idealists, wary of both military solutions and outright aggression, remained deeply uncomfortable with the entire concept of maintaining peace through armed deterrence alone.

Realism: Power as the Only Real Currency

Realism developed as a direct rebuttal to idealism’s optimism, built by thinkers including Machiavelli, Max Weber, E.H. Carr, Frederick Schuman, and Arnold Wolfers, among others. Where idealists put their faith in law and moral improvement, realists put their faith in the plain fact of power. Hans Morgenthau, one of realism’s most influential voices, captured the school’s core claim in a single line: national interest and power are bound together as the basic organizing concept of political theory itself.

Realist theory rests on a small number of hard assumptions. States, in this view, never achieve a genuine harmony of interests with one another – every state is perpetually working to secure its own interests, and that pursuit is precisely what generates conflict between them. A state’s foreign policy is shaped above all by its actual capabilities, whether political, military, or otherwise, rather than by its stated principles. States act to preserve their own freedom of action and self-determination wherever they can. Because realist analysis treats international behavior as something close to a mechanical, almost deterministic process, it leaves little room for judging state behavior against a moral standard – states do what their power and interests dictate, not what ethics would prefer. And where realists do accept the idea of balancing power between states to preserve peace – a concept idealists also embraced in their own way – the key difference is method: idealists wanted that balance achieved through moral and legal means, while realists expected it to be maintained through the hard mechanics of military and political power.

Two Schools, One Discipline

In practice, international institutions and international law have done real, if limited, work preserving world peace – but because they generally lack any independent force to back them up, their actual capacity to constrain powerful states has stayed weak, which is exactly why national interest remains the thing states actually organize their behavior around, whatever their public commitments to international law might suggest. It was the ongoing tension between these two schools – idealism’s moral ambition and realism’s hard-nosed skepticism – that gave international relations enough intellectual substance to mature into a genuine university discipline. Idealism has traditionally appealed to a certain kind of student drawn to how the world ought to work; realism has appealed to those more interested in describing how the world actually does work, and in using that unsentimental description to address real, present-day problems more directly than idealism, on its own, has generally managed to do.