The Archidamian War was the first phase of the Peloponnesian War, fought between the city-states of Athens and Sparta from 431 to 421 BCE. Named after the Spartan king Archidamus II, this conflict was characterized by annual invasions of Attica by Spartan forces and Athenian naval raids on the Peloponnesian coast. The war ended with the Peace of Nicias in 421 BCE, which temporarily halted hostilities but did not resolve underlying tensions. This period saw significant military strategies and political maneuvers, setting the stage for the later phases of the Peloponnesian War.