War fought between the two leading city-states in ancient Greece, Athens and Sparta.
Each stood at the head of alliances that, between them, included nearly every Greek city-state.
Athens - Delian League -> An alliance of city-states led by Athens, was, in fact, an empire that included most of the island and coastal states around the northern and eastern shores of the Aegean Sea.
Sparta - Peloponnesian League -> An alliance of independent states that included most of the major land powers of the Peloponnese and central Greece, as well as the sea power Corinth
Thus, the Athenians had the stronger navy and the Spartans the stronger army. The war occurred at the height of Athenian influence during the Classical period and ended with the defeat of Athens.
The fighting engulfed virtually the entire Greek world, and it was properly regarded by Thucydides, whose contemporary account of it is considered to be among the world’s finest works of history, as the most momentous war up to that time