The Acarnanians were of great service in maintaining the supremacy of Athens in the western part of Greece, and they distinguished themselves particularly in 426 BC, when they gained a signal victory under the command of Demosthenes over the Peloponnesians and Ambraciots at the Battle of Olpae. At the conclusion of this campaign they concluded a peace with the Ambraciots, although they still continued allies of Athens In 391 BC we find the Acarnanians engaged in war with the Achaeans, who had taken possession of Calydon in Aetolia; and as the latter were hard-pressed by the Acarnanians, they applied for aid to the Lacedaemonians (Spartans), who sent an army into Acarnania, commanded by King Agesilaus. The latter ravaged the country, but his expedition was not attended with any lasting consequences, whilst the cities of Acarnania surrendered to the Lacedaemonians under Agesilaus, and continued to be Spartan allies for a time, they joined the Second Athenian League in 375 BC. The Acarnanians later sided with the Boeotians in their fight against Sparta, and with Athens against Philip II of Macedon at Chaeronea.