426 BCE

An Athenian army under Nicias, Hipponicus and Eurymedon defeats a combined Tanagran and Theban army in the Battle of Tanagra. Demosthenes unsuccessfully besieges the Corinthian colony of Leukas. As a result, he does not return to Athens, fearing for his life. However when, later in the year, Ambracia invades Acarnania, and the Acarnanians seek help from Demosthenes, who is patrolling the Ionian Sea coast with twenty Athenian ships, he reaches the Athenian naval base in the Gulf of Corinth at Naupactus and secures it just in time to defend it against a large Spartan army from Delphi under Eurylochus which has come to assist the Ambraciots. Demosthenes defeats the Spartan army and Eurylochus is killed during the Battle of Olpae. The Acarnanians and Ambraciots then sign a peace treaty. The Athenian leader Cleon and Athenian general Demosthenes revitalise the city's military and naval forces despite opposition from Nicias, a rich merchant and soldier, and his supporters.

In the 420s BC, the 5th century BC.