The Second Peloponnesian War (431–404 BC), often called the Peloponnesian War, was fought between Athens and Sparta and their respective allies for the hegemony of the ancient Greek world. The war remained undecided until the later intervention of the Persian Empire in support of Sparta. Led by Lysander, the Spartan fleet (built with Persian subsidies) finally defeated Athens, which began a period of Spartan hegemony over Greece.
Historians have traditionally divided the war into three phases. The first phase (431–421 BC) was named the Ten Years War, or the Archidamian War, after the Spartan king Archidamus II, who invaded Attica several times with the full Hoplite army of the Peloponnesian League, the alliance network dominated by Sparta (then known as Lacedaemon). The Long Walls of Athens rendered this strategy ineffective, while the superior navy of the Delian League (Athens' alliance) raided the Peloponnesian coast to trigger rebellions within Sparta. The precarious Peace of Nicias was signed in 421 BC and lasted until 413 BC. Several proxy battles took place during this period, notably the battle of Mantinea in 418 BC, won by Sparta against an ad-hoc alliance of Elis, Mantinea (both former Spartan allies), Argos, and Athens. The main event was the Sicilian Expedition, between 415 and 413 BC, during which Athens lost almost all its navy in the attempt to capture Syracuse, an ally of Sparta.
