The first important contributor to ‘international’ thought is usually considered to be Thucydides. Though Herodotus is the “father of history” and it was Socrates that first brought philosophy ‘down from the heavens’ and into the agora, Thucydides was the first to deal with the relations among and between political communities in a theoretical manner.
Thucydides’ most important work is the History of the Peloponnesian War, which recounts the 27-year struggle in the 5th century BC between the city-states of Athens and Sparta. Perhaps the most famous element of the book is its account of the war’s cause, which Thucydides describes as the “growth in power of Athens, and the alarm which this inspired in Sparta.” Immediately clear to students of international relations is the consonance of this explanation with what Kenneth Waltz would call “third image” theory. According to Thucydides, it was neither the malign nature of any of the human beings involved, nor the authoritarian character of the Spartan regime, but changes in the relative distribution of power in the ancient Greek international-political system (if you will), that caused the war. One begins to see why so many courses start here.
As any classicist will tell you, Thucydides is more complicated than this. But it is true that some of the most dramatic passages in the History lend themselves to realist hagiography. Consider the so-called ‘ Melian dialogue‘ — perhaps the book’s second most famous passage — in which the Athenian envoy to Melos, a much less powerful city-state, informs his counterpart: “you know as well as we do that right, as the world goes, is only in question between equals in power, while the strong do what they will and the weak suffer what they must.”
This is an early argument for the primacy of power and security in international relations. Without question, it echoes one of the most important passages in political thought of any kind, the famous intrusion in Book 1 of Plato’s Republic by the sophist Thrasymachus, who advances the immoralist thesis that “justice is [merely] the advantage of the stronger”, and “injustice, if it is on a large enough scale, is stronger, freer, and more masterly than justice'”. Ultimately, it is this challenge that motivates what takes up the vast majority of the Republic: the attempt by Socrates and his friends to construct an ideally just “city in speech.”
Largely on the merit of that attempt, Plato is considered one of the first important political thinkers in the Western tradition. Many, however, are unaware of his ‘international’ thought, where he emerges as a rival to Thucydides. In the first Book of the Republic, Socrates begins to talk about matters of justice among city states, but is interrupted by Thrasymachus. The topic of war then re-surfaces in Books 2 and 3, where Socrates identifies its origins in the desire for “the customary luxuries” and appoints a warrior class of guardians whose profession is “the art of war.” But Socrates never clarifies in the Republic what this ‘art of war’ means in practice and how it serves justice (as it must, as part of the ideally just city). For that, luckily, there are the other dialogues: Timaeus, The Laws, and the mostly lost Critias.
In these three dialogues, Plato turns directly to what looks to us like international relations. In Timaeus and Critias (which are set on the day after the conversations that appear in the Republic), Socrates expresses his dissatisfaction with the ideally just city that he and his friends just constructed, complaining that it “is like seeing beautiful creatures at rest, and ignores the activities for which they appear to be formed.” As the discussion then immediately takes up the mythological war between an ideal-typical ur-Athens and Atlantis, it seems likely that, for Plato, international relations are precisely these activities for which city-states “appear to be formed.” One prominent scholar has even argued that the theme of Critias (of which only fragments survive) was, in fact, “a theoretical discussion of international relations.” In any event, these arguments put the ‘international’ question very near the center of Plato’s project.
Though we will probably never know what the fragmentary Critias contained, Plato can still be as foundational a figure for international thought as Thucydides. While Thucydides is usually conscripted into the service of one school of thought in particular, Plato provides a more pluralist point of departure. Conclusions about what Plato actually believed or recommended are often elusive, but the full gamut of contemporary approaches to international relations — and then some — are recognizable in his writings.
In Book 1 of The Laws, for example, realists will find an ally in the character Cleinias, who argues that “what most men call peace is really only a fiction, and that in cold fact states are by nature fighting an undeclared war against every other state.” Book 3, which is a speculative history of the development of ‘international’ norms among Greek (but not other) city-states, is useful fodder for English School theorists, constructivists, and cultural realists alike. And this is only the tip of the iceberg.
Though starting with Plato instead of Thucydides may seem an academic matter, we should not underestimate the power of the idea — to which starting with Thucydides lends credence — that 2500 hundred years ago in radically different circumstances, the first ‘international’ thinker was already a realist, or a liberal, or whatever else. Plato is the perfect antidote to this.