The Achaean League was a Hellenistic-era confederation of Greek city-states on the northern and central Peloponnese. The league was named after the region of Achaea in the northwestern Peloponnese, which formed its original core. The first league was formed in the fifth century BC. The second Achaean League was established in 280 BC. As a rival of Antigonid Macedon and an ally of the Roman Republic, the league played a major role in the expansion of Rome into Greece. This process eventually led to the League's conquest and dissolution by the Romans in 146 BC.

In classical antiquity, the Hellenistic period covers the time in Mediterranean history after Classical Greece, between the death of Alexander the Great in 323 BC and the death of Cleopatra VII, followed by the emergence of the Roman Empire, as signified by the Battle of Actium in 31 BC and the conquest of Ptolemaic Egypt the following year. The Ancient Greek word Hellas was gradually recognized as the name for Greece, from which the word Hellenistic was derived. "Hellenistic" is distinguished from "Hellenic" in that the latter refers to Greece itself, while the former encompasses all ancient territories under Greek influence, in particular the East after the conquests of Alexander the Great.