For the complete documentation index, see llms.txt.Skip to main content
The Peloponnesian War was fought between 431 and 404 BCE between two coalitions of Greek city-states: the Delian League, led by democratic and maritime Athens, and the Peloponnesian League, led by oligarchic and land-based Sparta. The primary contemporary account is Thucydides' History of the Peloponnesian War, supplemented for the final years by Xenophon's Hellenica.
Historians traditionally divide the war into three phases:
The war is foundational to the study of international relations. Thucydides' attribution of the war's cause to "the growth of the power of Athens, and the alarm which this inspired in Lacedaemon" underpins modern realist theory and the concept of the Thucydides Trap popularized by Graham Allison. The Melian Dialogue (Book V) is routinely cited as an early articulation of power politics: "the strong do what they can and the weak suffer what they must."
The conflict ended Athenian hegemony, installed the short-lived oligarchy of the Thirty Tyrants in Athens, and left the Greek world weakened ahead of Macedonian ascendancy in the following century.
Sparta and the Peloponnesian League won, forcing Athens to surrender in 404 BCE, dismantle its long walls, and dissolve the Delian League. Spartan-backed oligarchs known as the Thirty Tyrants briefly ruled Athens.
Thucydides framed the war as caused by Sparta's fear of rising Athenian power, a formulation foundational to realist theory and to modern debates about power transitions, including Graham Allison's 'Thucydides Trap.'
Although neutral early on, the Achaemenid Empire financed Spartan naval construction in the war's final phase under satraps Tissaphernes and Pharnabazus, and later Cyrus the Younger, in exchange for influence over the Ionian Greek cities.