Niccolò Machiavelli (1469–1527) remains one of the most provocative and influential political thinkers in Western history—a Florentine diplomat, historian, philosopher, and civil servant whose writings helped lay the foundations for modern political science and, crucially, the realist tradition in international relations. Born on May 3, 1469, in Florence, Machiavelli grew up during the Italian Renaissance, a period marked by artistic flourishing, intellectual revival, and intense political fragmentation. Italy at the time was not a unified nation but a patchwork of competing city‑states—Florence, Venice, Milan, Naples, and the Papal States—each vying for influence while foreign powers like France and Spain intervened aggressively in Italian affairs. This volatile environment shaped Machiavelli’s worldview and provided the raw material for his later political theories.

Machiavelli entered public service in 1498, shortly after the fall of the fiery preacher Girolamo Savonarola. He was appointed secretary to the Second Chancery of the Florentine Republic, a position that placed him at the heart of diplomatic and military affairs. For fourteen years, he traveled across Europe as a diplomat, meeting rulers, observing courts, and negotiating on behalf of Florence. These experiences exposed him to the brutal realities of power politics—alliances made and broken, states rising and falling, and leaders who succeeded not through virtue in the moral sense but through strategic calculation, deception, and force.

His diplomatic missions brought him into contact with some of the most formidable political actors of his time, including Cesare Borgia, whose ruthless efficiency and political cunning left a deep impression on Machiavelli. These encounters convinced him that political success depended not on idealistic moral principles but on a clear‑eyed understanding of human nature, necessity, and power.

In 1512, the Medici family returned to power in Florence, overthrowing the republic Machiavelli had served. He was dismissed, imprisoned, and tortured on suspicion of conspiracy. After his release, he retreated to his family estate at Sant’Andrea in Percussina. It was during this enforced political exile that he wrote his most famous work, The Prince, completed around 1513 but published posthumously in 1532. Although often interpreted as a manual for tyrants, The Prince is better understood as a study of political survival in a world governed by uncertainty, ambition, and conflict.

Machiavelli’s contributions to international relations emerge most clearly from this realist orientation. He rejected the utopianism of earlier political thinkers and instead grounded his analysis in what he called “the effectual truth” of politics—how states actually behave rather than how they ought to behave. Scholars note that “the whole drift of his work is toward a political realism, unknown to the formal writing of his time”. In this sense, Machiavelli stands alongside Thucydides and later Hobbes as a foundational figure in the realist tradition.

Several key themes in Machiavelli’s writings have become central to international relations theory:

1. The Primacy of Power and Security

Machiavelli argued that the survival of the state is the highest political good. Everything else—morality, tradition, even justice—must be subordinated to the preservation of political order. This emphasis on security as the core interest of states is a defining feature of realism and remains central to IR scholarship today.

2. Human Nature as a Driver of Political Behavior

Machiavelli’s view of human nature was famously pessimistic. He believed people are driven by fear, ambition, and self‑interest—traits that shape not only domestic politics but also the behavior of states on the international stage. As one scholar notes, Machiavelli saw fear as “the greatest master” in foreign policy.

3. The Interdependence of Domestic and International Politics

Long before modern IR theorists articulated the “two‑level game,” Machiavelli recognized that domestic stability is a prerequisite for effective foreign policy. A state torn by internal conflict cannot project power abroad. Conversely, foreign threats can reshape domestic institutions. This insight appears throughout The Discourses and his diplomatic correspondence.

4. The Role of Military Power

Machiavelli insisted that “good laws and good arms” are the twin foundations of a strong state. He distrusted mercenaries and auxiliaries, arguing that a state must rely on its own military forces to ensure independence. This emphasis on self‑help echoes the core realist assumption that states must provide for their own security in an anarchic international system.

5. The Instability of Alliances and International Arrangements

Machiavelli observed that alliances are fragile, shaped by shifting interests rather than loyalty or shared values. He warned that neutrality is often dangerous and that states must be prepared to adapt quickly to changing circumstances. These ideas anticipate modern theories of balance of power and alliance politics.

Beyond The Prince, Machiavelli’s Discourses on Livy, The Art of War, and History of Florence contain extensive reflections on foreign policy, diplomacy, and interstate conflict. His letters and dispatches reveal a keen analytical mind grappling with the complexities of international politics in a multipolar world.

Machiavelli died on June 21, 1527, in Florence, just weeks after the city fell to imperial forces. Although his name later became synonymous with political deceit, his true legacy is far more nuanced. He sought not to corrupt politics but to understand it—to strip away illusions and reveal the forces that shape human affairs.

Today, Machiavelli is widely regarded as one of the forefathers of modern realism in international relations. His insights into power, fear, ambition, and the interplay between domestic and foreign politics continue to inform the study of global affairs. In a world still marked by rivalry, uncertainty, and the struggle for security, Machiavelli’s work remains as relevant as ever.

If you are interested in learning more about this topic, you will enjoy our podcast series, How the World Works, where we explore the field of International Relations. 

International relations has always been, at its core, an attempt to make sense of why nations compete, cooperate, and sometimes collide. Long before the field had a name, thinkers were trying to decode the logic of power—why states rise, why they fall, and why peace so often slips through human fingers. From the battlefields of ancient Greece to the diplomatic chessboards of the Cold War, five major perspectives have defined this long intellectual arc.

1. Classical Realism — Thucydides and the Tragic Logic of Power

The story begins with Thucydides, the exiled Athenian general whose *History of the Peloponnesian War* is widely considered the first great text of international relations. His account of the conflict between Athens and Sparta is not just a chronicle of battles; it is a study of fear, ambition, and the unforgiving nature of an anarchic world. Scholars note that Thucydides provided “the foundations of what has been called in modern times Realpolitik or political realism”.

In the famous Melian Dialogue, the Athenians declare that “the strong do what they can and the weak suffer what they must”—a line that has echoed through centuries of strategic thought. For Thucydides, the international arena is defined by the absence of a higher authority, the primacy of self‑interest, and the tragic inevitability of conflict when rising and established powers collide. Modern realists—from Hans Morgenthau to Henry Kissinger—still draw on his insights.

2. Renaissance Realism — Machiavelli and the Effectual Truth of Politics

Nearly two millennia later, Niccolò Machiavelli sharpened realism into something colder and more clinical. Writing in the fractious world of Renaissance Italy, he observed firsthand how states maneuvered for advantage amid shifting alliances and foreign invasions. His work helped shape what scholars call “Classical Realism,” a tradition that includes Thucydides, Hobbes, and later Kissinger.

Machiavelli’s contribution was to strip politics of moral pretenses. In The Prince and The Discourses, he argued that rulers must understand the world as it is, not as they wish it to be. Power, he insisted, rests on military strength, strategic deception, and the ability to adapt to fortune’s turns. His realism was not cynicism for its own sake; it was a call to confront the “effectual truth” of political life. In international relations, this meant recognizing that states act out of necessity, not virtue.

3. Liberal Internationalism — The Hope for Cooperation After Catastrophe

If realism is the study of limits, liberalism is the study of possibilities. After World War I, as scholars sought alternatives to the balance‑of‑power politics that had failed so catastrophically, a new perspective emerged: liberal internationalism. It argued that war was not inevitable and that institutions, law, and economic interdependence could tame the anarchic system.

The discipline of international relations itself is often traced to this moment, with the establishment of the first academic chair in the field after the war. Liberal theorists believed that collective security—embodied in the League of Nations—could replace the old logic of rivalry. Though the League faltered, the liberal vision endured, later shaping the United Nations, NATO, and the post‑1945 economic order.

Liberalism’s core claim is that states are not doomed to perpetual conflict. Cooperation is possible when institutions reduce uncertainty, when democracies restrain aggression, and when trade binds nations together. It is a hopeful counterpoint to realism’s darker assumptions.

4. Neorealism and Neoliberalism — The Cold War’s Structural Turn

By the mid‑20th century, realism and liberalism were both reimagined through a more scientific lens. The Cold War’s stark bipolarity encouraged scholars to think in terms of systems, structures, and predictable patterns.

Kenneth Waltz’s Theory of International Politics (1979) pioneered neorealism, arguing that the structure of the international system—not human nature—drives state behavior. In an anarchic world, states must rely on self‑help, balance against threats, and prioritize survival. Power is measured not only in armies but in the distribution of capabilities across the system.

Neoliberalism (or liberal institutionalism) emerged as neorealism’s intellectual rival. Scholars like Robert Keohane and Joseph Nye argued that even in an anarchic world, institutions matter. They reduce transaction costs, create expectations, and allow cooperation to flourish even among self‑interested states. Neoliberalism did not reject realism; it refined it, suggesting that states can pursue absolute gains—not just relative ones—when institutions stabilize expectations.

Together, neorealism and neoliberalism defined the theoretical battleground of late‑20th‑century IR.

5. Constructivism and the Power of Ideas — A New Lens for a New Era

As the Cold War ended, something unexpected happened: the system changed without a shot fired. The Soviet Union collapsed, Germany reunified, and long‑standing alliances reshaped themselves. Material power alone could not explain these transformations.

Enter constructivism, the third major framework of modern IR. Emerging in the late 1980s and 1990s, constructivism argued that international politics is shaped not only by material forces but by ideas, identities, and social norms. Scholars such as Alexander Wendt and Martha Finnemore helped pioneer this approach.

Constructivism’s core insight is simple but profound: states act based on who they believe they are and what they believe others are. Anarchy, Wendt famously wrote, “is what states make of it.” The U.S. does not fear British nuclear weapons the way it fears North Korean ones—not because of capabilities, but because of identities and relationships.

Constructivism opened the door to studying nationalism, human rights, culture, and ideology as drivers of global politics. It explained why norms like sovereignty, humanitarian intervention, and nuclear restraint evolve over time.

The Kissinger Synthesis — Realism for the Modern Age

Henry Kissinger, the diplomat‑scholar who helped steer U.S. foreign policy during the Cold War, stands as a bridge between classical realism and contemporary strategic thought. His work draws heavily on Thucydides and the realist tradition, but he also understood the importance of diplomacy, perception, and psychological nuance.

Kissinger’s statecraft emphasized balance of power, spheres of influence, and the need for order in a world prone to chaos. Yet he also recognized that legitimacy—shared understandings of acceptable behavior—is essential for stability. In this sense, his perspective blends realist and constructivist insights, making him one of the most influential strategic thinkers of the modern era.

A Living Conversation

From Thucydides’ stark realism to Kissinger’s strategic pragmatism, from liberal hopes for cooperation to constructivist attention to identity, the study of international relations has evolved alongside the world it seeks to explain. These perspectives do not replace one another; they coexist, offering different lenses for different moments.

In a century defined by rising powers, technological upheaval, and renewed geopolitical rivalry, the old questions remain. Why do states fight? How do they cooperate? And what, if anything, can prevent history from repeating itself?

The answers, as always, depend on which lens we choose to look through.

If you are interested in learning more about this topic, you will enjoy our podcast series, How the World Works, where we explore the field of International Relations.

Thucydides (c. 460–c. 400 BCE) stands as one of the most influential thinkers of the ancient world—an Athenian historian, general, and analyst whose work shaped not only the study of history but the very foundations of modern international relations. Born in the Athenian deme of Halimous to a father named Olorus, who likely had Thracian aristocratic connections, Thucydides grew up in a world defined by the rise of Athenian power and the tensions that would soon erupt into the Peloponnesian War. Although little is known about his early life, later accounts suggest he may have encountered the historian Herodotus as a youth, an experience that supposedly stirred his passion for inquiry and historical writing.

Thucydides emerged into public life as a member of the Athenian elite, connected through family ties to influential figures such as Miltiades and Cimon. His wealth and status were further reinforced by his ownership of gold mines in Thrace, a resource that granted him both influence and strategic importance during the war between Athens and Sparta. When the Peloponnesian War broke out in 431 BCE, Thucydides was already old enough to grasp its significance and begin documenting its events with the meticulous eye of a soldier‑scholar.

His firsthand experience in the conflict would shape both his life and his intellectual legacy. In 424 BCE, he was elected stratēgos, a high-ranking military commander, and dispatched to defend the strategically vital city of Amphipolis. His failure to prevent its capture by the Spartan general Brasidas led to his exile from Athens for twenty years—a punishment that would ultimately become a gift to history. As Thucydides himself later wrote, exile granted him “leisure to observe affairs more closely” and the unique ability to move among both Athenian and Peloponnesian allies, gathering information from all sides of the conflict.

This dual perspective became the backbone of his monumental work, The History of the Peloponnesian War, a text that not only chronicled the conflict but revolutionized the practice of historical inquiry. Unlike Herodotus, who incorporated myth, divine causation, and cultural storytelling, Thucydides pursued what he called a “possession for all time”—a rigorous, evidence‑based account grounded in human motivations, political necessity, and the dynamics of power. For this reason, he is often called the “father of scientific history”.

Yet Thucydides’ influence extends far beyond historiography. He is widely regarded as the founding figure of political realism, the school of thought that views international politics as a struggle for power shaped by fear, self‑interest, and the pursuit of security. His analysis of the Peloponnesian War is not merely a narrative of battles but a profound exploration of how states behave under pressure, how leaders make decisions, and how power imbalances drive conflict.

One of the most famous examples of his realist insight is the Melian Dialogue, in which Athenian envoys bluntly assert that “the strong do what they can and the weak suffer what they must.” This stark articulation of power politics has become a foundational text in international relations theory, illustrating the logic of coercion, deterrence, and the tragic consequences of idealism in an anarchic world system. The dialogue remains required reading in military academies and political science programs worldwide.

Thucydides also offered a penetrating analysis of human nature, arguing that fear, honor, and interest—what later scholars would call the “Thucydidean triad”—drive both individuals and states into conflict. His account of the plague in Athens, the civil war in Corcyra, and the rise of demagogues like Cleon reveals how crises expose the darker impulses of human behavior, eroding norms and destabilizing political communities. These insights continue to inform contemporary discussions of war psychology, state collapse, and the fragility of democratic institutions.

His portrayal of Pericles, whom he admired as a model of prudent leadership, further underscores his contribution to political theory. Thucydides’ reconstruction of Pericles’ Funeral Oration remains one of the most studied speeches in Western literature, offering a vision of democratic values, civic duty, and national identity that continues to resonate today. At the same time, his critique of Athens’ later leaders highlights the dangers of populism, strategic overreach, and the erosion of disciplined statecraft.

Thucydides’ life after his exile remains obscure. Ancient sources suggest he may have returned to Athens after its defeat in 404 BCE, possibly due to a law passed by the statesman Oenobius, but the details are uncertain. His History ends abruptly in 411 BCE, leading scholars to conclude that he died before completing it, perhaps violently while traveling back to Athens.

Despite the gaps in his biography, Thucydides’ intellectual legacy is unmistakable. His work laid the groundwork for realist thinkers from Machiavelli to Hobbes to Hans Morgenthau. His insights into power transitions have shaped modern theories such as the “Thucydides Trap,” which examines the likelihood of war when a rising power threatens to displace an established one. His insistence on empirical observation, rational analysis, and the centrality of human nature continues to guide scholars, diplomats, and military strategists.

Thucydides sought to understand not only what happened in the Peloponnesian War but why it happened—and in doing so, he uncovered patterns of behavior that transcend time and culture. His work remains a mirror in which every generation can see its own struggles with power, fear, ambition, and the fragile pursuit of peace.

If you are interested in learning more about this topic, you will enjoy our podcast series, How the World Works, where we explore the field of International Relations.