Sparta was focused on the exception to the arrogance and stolen treasury of the Athenians.
War started
Athens focused on wealth, prestige, and power wasn't well by other states like Sparta. Athens had the stronger Navy, while Sparta has the stronger Army.
War continued
Athens and Sparta declared war
War Ended
Pericles strategy was to avoid land battles and strike Sparta and it is allied from the sea
Spartans marched into the Athenian territory, after the 2nd year of the war the plague struck Athens. Sparta and Athens worn down the war in 421 B
Athenians able to fend of Spartan attacks for 9 years before their allies surrendered to Sparta and the empire fell.