Achaia in the Bible Encyclopedia - ISBE

a-ka'-ya (Achaia): The smallest country in the Peloponnesus lying along the southern shore of the Corinthian Gulf, north of Arcadia and east of Elis. The original inhabitants were Ionians, but these were crowded out later by the Acheans, who came from the East. According to Herodotus, the former founded twelve cities, many of which retain their original names to this day. These cities were on the coast and formed a confederation of smaller communities, which in the last century of the independent history of Greece attained to great importance (Achaean League). In Roman times the term Achaia was used to include the whole of Greece, exclusive of Thessaly. Today Achaia forms with Elis one district, and contains a population of nearly a quarter of a million. The old Achean League was renewed in 280 BC, but became more important in 251, when Aratus of Sicyon was chosen commander-in-chief. This great man increased the power of the League and gave it an excellent constitution, which our own great practical politicians, Hamilton and Madison, consulted, adopting many of its prominent devices, when they set about framing the Constitution of the United States. In 146 BC Corinth was destroyed and the League broken up (see 1 Macc 15:23); and the whole of Greece, under the name of Achaia, was transformed into a Roman province, which was divided into two separate provinces, Macedonia and Achaia, in 27 BC.

Link: https://bible-history.com/isbe/A/ACHAIA/