What was the name of the alliance led by Sparta during the classical Greek period?

The alliance led by Sparta during the classical Greek period was the Peloponnesian League.

The Peloponnesian League was a coalition of Greek states, many of them in the Peloponnese, organized under Spartan leadership. It was not a single unified state. Member communities generally retained their own governments, while Sparta coordinated military action and diplomacy through meetings of allied representatives.

The league became Sparta’s principal power base and an important counterweight to Athens and the Delian League. Its members included Corinth and other communities whose interests sometimes differed from Sparta’s. This mixture of cooperation and independence helps explain why league decisions could be difficult to enforce.

The Peloponnesian War began in 431 BCE after escalating conflict between the Athenian and Spartan spheres of influence. Sparta and its allies eventually defeated Athens in 404 BCE, although the war badly weakened the wider Greek world. Spartan dominance did not last permanently: Thebes defeated Sparta at Leuctra in 371 BCE.