“We don’t care about your stupid FONOPs.” That’s what a group of retired People’s Liberation Army Navy (PLAN) officers told an American interlocutor recently. They referred, of course, to the “freedom-of-navigation” patrols the U.S. Navy has undertaken in the South China Sea of late. Most recently the destroyer USS Decatur mounted a challenge in the Paracel Islands. But if not FONOPs, what does get Chinese blood pumping? “We care about our ability to project power,” quoth the doughty seafarers. “Law is only as good as it can be enforced.”

How refreshingly Thucydidean! Or, more precisely, how refreshingly Athenian. Odd, isn’t it, how politics makes strange bedfellows? And few bedfellows could be stranger than the compact democratic city-state from Greek antiquity and the sprawling one-party authoritarian state that is contemporary China. But however radically they differ in domestic rule, classical Athens and present-day China operate from similar principles in the international realm.

These hardbitten principles derive from the conviction that law and justice go no further than arms can take them. They find their clearest expression in the “Melian Dialogue,” wherein Athens makes a weaker neighbor an offer it can’t refuse—join the Athenian empire or die—then metes out a harsh fate when the neighbor does refuse. The Melian Dialogue isn’t just a historical episode. It’s a parable about the consequences of too lopsided a power mismatch against an amoral foe.

Thucydides is the premier chronicler of the Peloponnesian War and an eyewitness to many of the war’s events. In the father of history’s telling, Athenian statesmen are forthright about the exploitative nature of the system they superintend. In the early years of the Peloponnesian War, “first citizen” Pericles reminds his countrymen that Athens is a tyranny abroad, regardless of how liberally it comports itself at home. It may have been wrong to seize an empire; it’s dangerous to let it go once it has been taken. Paybacks are hell.

Pericles knew whereof he spoke. Founded as a democratic alliance in the wake of the Persian Wars, the Athenian-led Delian League degenerated into a coercive empire as the fifth century B.C. wore on. Athens moved the league’s treasury from the island of Delos to Athens, stripped its allies of their navies, and forbade the allies to erect walls around their cities—walls that might empower them to defy Big Brother’s bidding. No ally was permitted to leave the empire.

That’s tyranny with a capital T. Brute power constitutes the prime mover impelling Athenian actions. Thucydides relates the tale of the fateful encounter between Athens and the island city-state of Melos. In so doing he lays bare Athenian motives.

Melos occupied a strategic offshore location near Athens’ archfoe Sparta, making the island an ideal outpost for naval operations. The Athenian assembly dispatched a delegation to wring surrender from them.

After entreating the Athenian ambassadors to allow them to maintain their neutrality, the islanders opt to defy the Athenian demands. Melos falls after a brief siege, whereupon the Athenian assembly votes to kill the adult male populace and enslave the women and children.

The Melian Dialogue reveals several undercurrents in Athenian power politics. First of all, the Athenian emissaries—much like our retired PLAN officers—maintain that questions of justice seldom arise in international politics absent a rough parity of arms between antagonists. This elemental reality is not lost on the Melians, who seem resigned to defeat from the beginning yet cling stubbornly to their independence. “We see that you have come prepared to judge the argument yourselves, and that the likely end of it all will be either war, if we prove that we are in the right, and so refuse to surrender, or else slavery.” Athens confronts them with a Catch-22.

The Athenians agree with the Melians’ grim prognosis, proclaiming that “the standard of justice depends on the equality of power to compel and that in fact the strong do what they have the power to do and the weak accept what they have to accept.” For Athenians this amounts to a divine law. “Our opinion of the gods and our knowledge of men lead us to conclude that it is a general and necessary law of nature to rule whatever one can.” Not only is this a permanent precept of international relations, but “anybody else with the same power as ours”—including the Melians—“would be acting in precisely the same way.”

A China of Athenian inclinations would be a domineering China, apt to bully Asian neighbors that can’t match up to Chinese diplomatic, economic, or military might. For a statement displaying a Melian tenor, look no further than Foreign Minister Yang Jiechi, who in 2010 told a meeting of the ASEAN Regional Forum: “China is a big country and other countries are small countries and that is just a fact.” We’re big, you’re small—get used to it. Take note, Asian countries, if you treasure your rights under the law of the sea.

And take note, America, if China stops believing in the U.S. military’s capacity to project power into Asian waters to uphold freedom of the sea. In all likelihood, FONOPs will remain necessary for years to come. But as the Chinese naval officers imply, these must be FONOPs that the People’s Liberation Army knows it cannot defeat. Simply showing up in verboten waters or skies garners little respect. Showing up there with ships, planes, and armaments that would prevail in combat is what wins respect from a Melian opponent.

Second, a powerful nation can use its armed might for a variety of purposes derived from the Thucydidean motives of fear, honor, and interest. An empire might, for instance, use its military power to acquire strategically placed territories. “[B]y conquering you,” proclaim the Athenian ambassadors, “we shall increase not only the size but the security of our empire.” For Athens there were obvious geostrategic advantages to wresting Melos from its inhabitants. The island was ideally positioned off the southeast coast of the Peloponnesus. Operating from bases on the island, the formidable Athenian navy could conduct operations along the Spartan periphery, amplifying the already dominant sea power of Athens.

The Athenians also wanted to make an example of Melos, which had stubbornly maintained its independence and in past years had taken up arms to resist the imperial will. Many of the allies had grown restive, weary of the high cost of war and the increasingly tyrannical character of Athens. The Athenians concluded they couldn’t allow the Melians to defy them for fear of emboldening other allies to seek liberty from imperial rule. “We rule the sea and you are islanders, and weaker islanders too than the others,” observe the Athenian emissaries; “it is therefore particularly important that you should not escape.”

Hegemonic states, then, prize consistency. It’s doubtful in the extreme that China will make exceptions to its claims to sovereignty over sea- and airspace. The Philippines or Malaysia is apt to be disappointed if it hopes to win forbearance by cozying up to China. Beijing might back off temporarily and for tactical reasons, as it seemingly has vis-à-vis Rodrigo Duterte’s Philippines. It would be a stunner if the Chinese Communist leadership gave in altogether and resumed keeping its commitments under the law of the sea.

Third, the side endowed with preponderant armed strength has the luxury of pursuing a harsh diplomacy in order to win without resort to arms. That’s the “acme of skill” in Chinese statecraft. It can attempt to browbeat a weaker opponent into submission by menacing it with the prospect of defeat and destruction.

This, as much as any coarsening of Athenian virtue during the course of protracted war, helps account for the ruthless, frankly immoral tone of the Athenian pronouncements. The Athenian ambassadors wave away the Melian petition for justice: “we on our side will use no fine phrases saying, for example, that we have a right to our empire because we defeated the Persians, or that we have come against you now because of the injuries you have done us—a great mass of words that nobody would believe.” Not persuasion but brute power was deployed at Melos.

China, likewise, is no stranger to chest-thumping when it thinks it enjoys an edge in diplomatic, economic, or military power. It can coerce or deter by disheartening seafaring states—dissuading them from trying to enforce their rights and prerogatives under the law of the sea and other accords. Beijing practices a bareknuckles form of winning-without-fighting.

Fourth, hope is not a strategy in international politics. The Melian representatives hold that, because their cause is just, they can trust to fortune or their Spartan kinsmen to intervene on their behalf and avert disaster. They maintain that “in war fortune sometimes makes the odds more level than could be expected from the difference of numbers of the two sides.” They also point to the geographic proximity of Sparta and the ethnic affinity between Spartans and Melians: “we think [the Spartans] would even endanger themselves for our sake and count the risk more worth taking than in the case of others, because we are so close to the Peloponnese that they could operate more easily,” and because “we are of the same race and share the same feelings.”