What was the main cause of the Peloponnesian War?
A.
The Spartans resented Athens' dominance over other city-states.
B.
The Peloponnesian people turned out to be even fiercer warriors than the Spartans, so they attacked.
C.
Sparta began building a navy and the Athenians responded.
D.
The other city-states decided to band together to defeat Sparta and Athens.