Thucydides is universally recognized as the progenitor of history. Yet he was far more than a chronicler striving for factual verification; he was a theorist of war. He sought to extrapolate from specific events to broader conclusions regarding the nature of human behavior and social agency.
His structuralist approach introduced the concept of the balance of power, which served as the operational principle of European diplomacy, within the Concert of Europe, from the seventeenth through the twentieth centuries. In this sense, Thucydides may be regarded as a founder of the social scientific project: the modern effort to apply scientific methods to the explanation of social phenomena. No such phenomenon has been scrutinized more closely than war, precisely because of its destructive potential.
By attributing the eruption of the Peloponnesian War between Athens and Sparta not to personal animosities or misunderstandings, but to the shifting balance of power and the fear the rise of Athens instilled in Sparta, Thucydides established himself as the first Realist thinker of international relations.
Given the hegemony of Realism in both academic theory and political practice, Thucydides’ work retains a powerful resonance. This is particularly true today, amid the revival of power politics following Donald Trump’s assumption of the U.S. presidency in January 2025 and the Russian invasion of Ukraine three years prior.
This essay casts a new light on Thucydides’ thinking—one that is truer to his original mission and more relevant to the contemporary world. By recasting Thucydides as a critic of Realism’s foundational assumptions, rather than its uncritical father, I aim to dismantle fundamental misunderstandings of his oeuvre that hinder the successful management of international relations. In doing so, I hope to unlock his full explanatory power and pedagogical wisdom for today’s policymakers.
In chronicling the history of the Peloponnesian War, which convulsed the Greek world of the fifth century BCE, Thucydides had two objectives. The first he stated explicitly in his opening passages: he wrote not for his contemporaries, but for eternity. His purpose was to help future generations understand the drivers of conflict and, by extension, how to avoid it.
His most celebrated insight was that the war was precipitated by a structural shift in power from Sparta to Athens and the fear this engendered among the Spartans. Thucydides was careful, however, to supplement the objective fact—the power transition—with a subjective element: the fear this shift provoked in Spartans, leading to their specific decision to check Athens’ rise through war.
Thucydides is a structuralist, but he is not a determinist. To him, structure constrains, but humans retain their agency—and with it, the freedom to choose their response. Herein lies his most vital lesson for the present: power transitions need not inevitably lead to war. Human actors, and specifically wise leaders, possess the agency to manage these transitions through non-conflictual means, thereby averting the catastrophe of total war.
Realists, however, often neglect this second half of his insight. They ascribe to Thucydides a rigid, hyper-structural determinism—a view that holds human leaders hostage to objective developments, rendering them incapable of positively influencing events.
This fatalism is dangerous. If one believes conflict is inevitable, conflict becomes inevitable. In such a cognitive trap, the only rational option for leaders is to prepare for war, a choice that immediately exacerbates the security dilemma of their neighbors. By arming for conflict, a state becomes an existential threat to others, who subsequently opt for their own arms accumulation. This cycle pushes a precarious equilibrium toward its eventual breaking point.
Yet, this determinist reading is not the most glaring omission in our modern understanding of Thucydides. The most critical element missing from contemporary analysis is an inexplicable indifference to his second goal. Thucydides sought not only to explain why the war began, but also why Athens lost and Sparta won.
This outcome was far from predetermined. At the war’s outbreak, Athens was indisputably the preeminent power in the classical Greek world. Thucydides leaves no doubt on this score. In the famous Pericles’ Funeral Oration, delivered at the end of the first year of the war, he portrays Athens in laudatory terms: the perfect human community, a true “city upon a hill,” to borrow the biblical metaphor.
In the words Thucydides attributes to Pericles, Athens is strong yet wise, daring yet restrained, wealthy in both material and cultural terms, pluralistic yet united. At the onset of hostilities, the historian has no doubt that the stronger, more confident party—buoyed by its navy, its treasury, and its web of alliances—is Athens, not the declining Sparta. And yet, Athens, Thucydides’ beloved city, ultimately fell. This paradox demands explanation. To resolve this contradiction, Thucydides delves deep into the Athenian polity and the devastating impact the war visited upon it.
For Thucydides, the verdict is clear: Athens was not defeated by Sparta; it was defeated by Athens. Its fall was a suicide, not an assassination. Athens lost the war as a result of its own unforced errors, not because of Spartan superiority.
Specifically, Athens lost due to the degradation of its polity and the decay of its democracy. For Thucydides, democracy is fragile, contingent on the temper of its citizens. War unleashes the basest elements of human nature and fuels irrationality.
Nowhere was this corrosive effect more evident than in its leadership. The wise statesmanship of Pericles was usurped by the rule of demagogues—men like Kleon and, above all, Alcibiades. These figures stoked populist impulses, misleading the Athenian Assembly into catastrophic decisions for their own short-term political gain. Worse, they did not hesitate to betray the state to evade accountability, as was famously the case with Alcibiades’ defection during the disastrous Sicilian expedition.
Athens lost because of itself. This is the most powerful and enduring lesson for the West as it confronts the challenges of today. The rise of China does not, in itself, mandate confrontation and Western defeat.
Despite the widespread alarmism pervasive in Washington and other capitals, the empirical reality remains clear: the West, if united, remains the preeminent global force. It commands more than half the world economy and accounts for three-quarters of global military spending and new research. China, by contrast, confronts decelerating growth rates and an inescapable demographic trap.
If the West is to fear any adversary, it should fear itself. In this instance, suicide is a far more probable cause of death than murder. The West is under attack from within.
The rise of extremism, populism, and ethno-nationalism—coupled with the broader crisis of liberal politics—has shaken the Western order far more profoundly than China’s foreign policy choices ever could. Brexit deprived the European Union of its second-strongest economy, a nuclear power, and a permanent seat on the UN Security Council. Donald Trump’s ill-guided neo-mercantilism and systematic assault on America’s European allies have fractured the Western alliance, delivering a strategic gift to Russia, China, and every rival of the liberal order. Furthermore, the ascendance of the far right—the AfD in Germany, Marine Le Pen in France, and Nigel Farage in the UK—is bound to exacerbate internal tensions, making unity and cooperation increasingly difficult to achieve.
In Thucydidean terms, Western societies are in the grip of a systemic overreaction. This anxiety stems from a confluence of factors: relative decline in power, the rise of Asia, the rapid expansion of a service economy—often perceived as structurally disadvantageous to the traditional male industrial workforce—and the subsequent disillusionment of those workers. These structural shifts are compounded by increased migratory flows and the proliferation of disinformation through social media. Our democracies are proving far more suicidal than prudent.
Brexit serves as a paradigmatic case study. By all accounts, it has devolved into an unmitigated disaster for Great Britain, severely damaging its economy and diminishing its global standing. More such disasters are bound to occur as electorates across the West appear disillusioned, while traditional parties seem incapable of arresting their own decline or countering the rise of a “politics of irrationality.”
Yet, Thucydides holds one final lesson for the power-hungry Realists of the present day who claim to understand the world better than “soft” idealists. This lesson is found in the most unexpected chapter of his work: the Melian Dialogue. This dialogue, recounting the negotiations between representatives of Athens and the island of Melos in 416 BCE, depicts the Athenian delegation demanding the surrender of the Melians with the brazen assertion that “the strong do what they can and the weak suffer what they must.” This specific passage from the Melian Dialogue—one of the many literary innovations Thucydides uses to illuminate opposing worldviews—has emerged as a foundational text in the canon of Realist literature.
Yet, one must be more discerning. Thucydides is rarely as straightforward as he appears. His dialogue is no endorsement of the Realist worldview; far from it. The exaggerated and naked assertions of the Athenians serve not as an endorsement, but as a denunciation. Crucially, however, this is not a denunciation in the moral sense. Morality is not Thucydides’ primary concern. For him, the Athenians are wrong not because they are “bad,” but because they have willingly disarmed themselves of the power of attraction and persuasion, relying instead solely on brute force and coercion.
For Thucydides, the Athens of 416 BCE is no longer the confident, optimistic, and attractive superpower of the Funeral Oration delivered some fifteen years earlier—a city possessing an abundance of both hard and soft power. In that earlier era, Athens was powerful not merely because it had the capacity to coerce, but, more importantly, because it had the capacity to persuade. Other Greek city-states did its bidding not out of fear or obligation, but out of admiration and their own free will. Athens was powerful because others desired to emulate it. The moment Athens loses its glow—the moment it must rely exclusively on brute force—it has become weak, and the end is near. Melos might be brutally subdued, but the act itself guarantees that others will rise up and resist.
This serves as the most devastating critique of today’s Trumpian logic. Donald Trump’s foreign policy is flawed not simply because it is immoral or illegal; many past U.S. presidents have made decisions that were questionable on both counts. His policy is flawed because it is self-defeating. It weakens America rather than strengthening it. Alliances are not burdens to be shed, but assets to be leveraged—a unique feature of America’s global standing that no rival enjoys.
Thucydides was the brilliant mind of an unprecedented era in human history. His penetrating critique of the human condition, his insight into social interactions, and his unique ability to fuse empiricism with theory make him a titan in the eternal human effort to understand ourselves. His wisdom holds vital truths for our present condition. Far from justifying the confrontational turn in U.S. foreign behavior, he cautions against arrogance and hubris. And he does so without moralizing. His world is one of interests, and in this interest-based reality, the paramount task for any actor is to distinguish between what is truly in their interest and what is merely the impulse of power.
