The Peloponnesian War (431-404 BCE) was a devastating conflict fought between Athens and its empire, and the Peloponnesian League, led by Sparta.

The primary cause of the war was Spartan fear of Athens's growing power and influence.

The war pitted Athens's dominant navy against Sparta's superior land army.

Early in the war, a devastating plague struck Athens, killing a large portion of its population, including its leader, Pericles.

A key turning point was Athens's disastrous Sicilian Expedition, a failed attempt to conquer Syracuse that crippled its military.

Sparta, with financial aid from Persia, eventually built a navy capable of challenging Athens at sea.

The war ended with the final defeat of the Athenian navy and the surrender of Athens in 404 BCE.

The Athenian historian Thucydides wrote a detailed and analytical account of the war.

The conflict left all of the Greek city-states weakened and exhausted.

This weakness paved the way for the subsequent conquest of Greece by Philip II of Macedon.