The Aetolian League was formed out of a tribalism of Aetolians, made up of small townships and rural communities, to which by about 250 covered most of central Greece north of the Gulf of Corinth.
The Aetolian league had taken possession of Delphi in 290 BC and fought off (according to Diodorus) 160,000 Gauls there in 279 BC. This collection of villages north of the Corinthian Gulf joined together for defense and plunder, increasing their votes on the Amphictyonic council from two to six in ten years.
Since then they dominated almost all of central Hellas, and that is why they had continuous conflicts with Macedon. Because of this they contacted the Romans later on to interfere in Hellas. The Aetolians had a bad name as they were feared pirates.
The council of all Aetolians assembled twice a year, and matters were voted by call. Besides this body the cities were proportional represented in the boule of 1000 people. The real decisions were made by a council of thirty, who were chosen from the boule, and the annually chosen strategos who was president of the League and commander of the army at the same time. The Aetolian League was tribal at first so that non-Aetolian cities could only be associated with the League by an isopoliteia-treaty.