what made war inevitable was growth of athenian power and
The Cause of the Peloponnesian War. The immediate cause of the Peloponnesian War was Corinthian opportunism. Thucydides is mistaken in his famous assertion that [w]hat made war inevitable was the growth of Athenian power and the fear which this caused in Sparta. Both powers had demonstrated a reluctance for head-on war over matters peripheral to their respective spheres of influence.