Aetolian League (Greek: Κοινὸν τῶν Αἰτωλῶν): confederation of Greek city states, focused on but not limited to western Greece. It was important in the third and early second centuries BCE.
In the Hellenistic Age, new confederations of Greek city states were created. Confederation itself was nothing new. In the Classical Age, poleis had been united by Sparta in the Peloponnesian League, by Athens in the Delian League, and by Thebes in the Boeotian League. What was new, was citizenship: people were citizen of both their own city state and the league. When people resettled from one polis to another, it was comparatively easy to change one's citizenship (isopoliteia).
Among the new leagues were the Nesiotic League (on the Aegean islands, protected by the Ptolemies), the Achaean League (on the northern Peloponnese), and the Aetolian League (in western Greece). The latter may have had its origins as a religious amphictyony, centered on a sanctuary in Thermos.
In 338 BCE, Philip II of Macedonia awarded the Aetolians (whether a league or not) with Naupactus. After the death of Philip's son Alexander (323 BCE), the Aetolians supported Athens in theLamian War against Macedonia. This was the beginning of a consistent anti-Macedonian policy, which gained momentum after the Aetolians took Delphi (301 BCE). Later, in 279, they defeated Celtic invaders. The Thebans found it wise to join the league in 245, although it later switched to an alliance with Macedonia.
The increasing power of the Aetolian League caused tensions with its neighbor on the other side of the Gulf of Corinth, the Achaean League, although the Aetolians were wiling to cooperate with the other confederation when it turned against Macedonia. In 239, the two leagues attempted to conquer Thessaly.
When, after the battle of Cannae (216) the Macedonian king Philip V allied his kingdom to the Carthaginian general Hannibal, the Romans allied themselves to Macedonia's eternal enemy. Together, Rome and Aetolia fought the First Macedonian War (214-205) and the Second Macedonian War (culminating in the battle of Cynoscephalae, 197). Fearing they became too close to its western ally, the Aetolian leaders attempted to become more independent and invited the Seleucid king Antiochus III the Great to help them, but during the Syrian War (192-188), the Romans defeated the foreign liberator and looted the Aetolian capital Ambracia (189) and forced to pay tribute.
There were serious disturbances inside the confederation, which lost its political significance. After the Third Macedonian War (172-168), it was reduced to the original land of the Aetolians. When the Romans reorganized Greece and Macedonia after the Fourth Macedonian War (150-148) and the Achaean War (146 BCE), Aetolia was humiliated by being included in the newly created province of Macedonia.