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Peloponnesian War

The Peloponnesian War was a major conflict in ancient Greece fought between Athens and Sparta and their respective alliances from 431 to 404 BCE.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 26, 2026|2 min read| Fact-checked

The Peloponnesian War was a major conflict in ancient Greece fought between Athens and Sparta and their respective alliances from 431 to 404 BCE. It ended with a Spartan victory and the dismantling of Athenian power, reshaping the balance of power in Greece.

Background and causes

Tensions grew from competition for power in Greece, especially Spartan fear of Athenian imperialism. Earlier disputes between the city-states and their allies helped bring down an earlier peace agreement.

Course of the war

The war is usually divided into phases, including the Archidamian War, a period of truce after the Peace of Nicias, and the final phase ending in Spartan victory. Major events included the plague in Athens, the Sicilian expedition, and the battle of Aegospotami.

Outcome and consequences

Athens surrendered in 404 BCE after losing its navy and being blockaded. The defeat ended Athenian imperial power and established Spartan dominance in Greece for a period.

Historical significance

The war is widely seen as one of the most important conflicts of the ancient world. Thucydides’ account of it is regarded as a landmark work of historical writing.

Key facts

  • The war was fought between the leading city-states of ancient Greece, Athens and Sparta.
  • It lasted from 431 to 404 BCE, with a brief truce in the middle.
  • The conflict involved alliances that drew in much of the Greek world.
  • Athenian naval strength and Spartan land power shaped the war’s strategy.
  • The war ended after the destruction of the Athenian fleet at Aegospotami and Athens’ surrender in 404 BCE.
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Canadian context

The Peloponnesian War is taught in Canadian history, classics, and political science courses as a foundational case study in interstate rivalry, alliance politics, and war in the ancient Mediterranean.

Frequently asked questions

When did the Peloponnesian War take place?
It lasted from 431 to 404 BCE.
Who fought in the Peloponnesian War?
Athens and its allies fought Sparta and its allies.
Why did the war begin?
A major cause was Spartan fear of Athenian power and imperialism, along with disputes involving allies on both sides.
Who won the Peloponnesian War?
Sparta won the war, defeating Athens in 404 BCE.
What was the result for Athens?
Athens lost its empire, and Sparta imposed the rule of the Thirty Tyrants.
Why is the war historically important?
It reshaped Greek politics and is known through Thucydides’ influential contemporary history.

References

  1. Encyclopaedia Britannica — https://www.britannica.com/event/Peloponnesian-War
    Supports: Date, participants, scope, and historical significance.
  2. Encyclopaedia Britannica — https://www.britannica.com/summary/Peloponnesian-War
    Supports: Causes, major phases, Athenian defeat, and aftermath.
  3. The Latin Library — https://www.thelatinlibrary.com/historians/narrative/peloponnesianwar.html
    Supports: General narrative of causes, duration, and Athens' surrender.
  4. History.com — https://www.history.com/articles/peloponnesian-war
    Supports: Summary of the war, outcome, and broader effects on Greece.