To understand how nations act, classical realists begin with a simple, unsettling premise: to understand the state, you must first understand human nature. Thinkers like the ancient Greek historian Thucydides, the Renaissance political theorist Niccolò Machiavelli, and the 20th-century scholar Hans Morgenthau shared a sober view of humanity. They observed a persistent, powerful drive in people—a desire to dominate, which they called the animus dominandi.

This isn't just a belief that people are inherently evil. It's a recognition that the lust for power is a fundamental, often predictable, force in human affairs. When this drive is scaled up from individuals to states, it creates an international environment where competition and conflict are always possible. States, led by people, will naturally seek to preserve themselves and increase their influence.

The most famous illustration of this is the Melian Dialogue, a passage in Thucydides' work. In it, the powerful Athenians confront the leaders of the small, neutral island of Melos. The Melians appeal to justice and fairness, but the Athenians are brutally direct. They dismiss appeals to morality, stating that in the real world, “the strong do what they can and the weak suffer what they must.” The Melians refuse to submit, and Athens conquers them, kills the men, and enslaves the women and children. It's a stark lesson in the Realist view of power trumping abstract ideals.

Centuries later, Hans J. Morgenthau, a German-American scholar who fled Nazi Germany, tried to systematize this worldview. He argued that international politics, like all politics, is a struggle for power. To make sense of it, he developed six principles of political realism, creating a framework for analyzing state behavior.

Morgenthau’s central idea is that statesmen think and act in terms of interest defined as power. This doesn't mean leaders are always aggressive warmongers. It means their primary responsibility is the survival of their state, and power is the means to ensure that survival. This creates a logical, rational way to understand why states act as they do, regardless of their leaders' personal morals, motives, or ideological preferences.

If leaders must prioritize power, does that mean morality has no place in foreign policy? For classical realists, the answer is complex. They draw a sharp line between private and public morality. A private citizen can afford to be self-sacrificing, but a leader is responsible for the lives and security of millions. A leader who applies abstract, universal moral principles—like turning the other cheek—to statecraft is failing in their primary duty to protect the state.

This is where the concept of prudence becomes the supreme virtue in politics. Prudence is the ability to weigh the consequences of different political actions. It's about foresight and caution. A prudent leader doesn't ask, “Is this action good or evil?” but rather, “What will be the effect of this action on my nation's power and security?”

Consider the 2003 invasion of Iraq. A classical realist might argue that the decision was imprudent. Not because it was necessarily immoral in a universal sense, but because its architects may not have fully weighed the long-term consequences for American power and regional stability. The goal of removing a dictator might seem noble, but if the result is a power vacuum, protracted insurgency, and the rise of new adversaries like Iran, then the action was a strategic failure. A prudent leader would have anticipated these potential outcomes.

Conversely, early U.S. diplomatic dealings with post-revolutionary Iran show moments of attempted prudence. While ideological differences were vast, some policymakers on both sides tried to engage based on national interest rather than pure hostility. These efforts were often undermined by domestic politics and mutual suspicion, but they illustrate the classical realist impulse to manage conflict through a sober calculation of interests, rather than through crusades based on moral abstractions.

Ultimately, classical realism offers a timeless and often uncomfortable lens for viewing the world. It forces us to confront the role of human nature in conflict and to value the careful, pragmatic exercise of power over grand, and often dangerous, moral certainty.