At the commencement of the Peloponnesian war Sitalces entered into alliance with the Athenians, and in 429 BC he invaded Macedon (then ruled by Perdiccas II) with a vast army that included 150,000 warriors from independent Thracian tribes (such as the Dii) and Paeonian tribes (Agrianes, Laeaeans).
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Sitalces enlarged his kingdom by successful wars, and it soon comprised the whole territory from Abdera in the south to the mouths of the Danube in the north, and from the Black Sea in the east to the sources of the Struma in the west.