Well according to Thusydides it was the fear and jealousy of Athens, the Pentecontaetia incident where the attempt to prevent Athens from rebuilding its walls was rebuffed, the resettlements of rebel helots by Athens on a strategic city of Naupactus and the corcyraen incidents.
The immediate incidents that led up to the war. The corcyraean incident, the siege of Potidaea and the Megarian degree.
note: Different sources have different views on the causes or place a higher regard for some in complaisant to others.
http://www.answers.com/Peloponnesian%20war
the power struggle between Athens and Sparta. Athens had emerged as a dominant naval power in the Aegean while Sparta was the leader of the Peloponnesian League. Tensions between the two city-states grew as they competed for influence and resources, eventually leading to the outbreak of the war.
. . . the Peloponnesian War .
Rivalry between Athens and its empire and the Peloponnesian League led by Sparta.
The Peloponnesian War was a conflict between the two city-states of Athens and Sparta .
The Peloponnesian War was between alliances of Greek city-states - Athens and its empire, and the Peloponnesian League led by Sparta.
Building tensions between Athens and its empire and the Peloponnesian League led by Sparta set up to oppose it, came to a head when Athens banned Peloponnesian League member Megara from trading within Athens' empire. This meant the ruination of Megara. The Peloponnesian League demanded an end to the ban, which a fully-confident Athens rejected. War ensued.
It was between Athens and its empire and the Peloponnesian League headed by Sparta.
The Peloponnesian War was , notably , between Athens and Sparta . A democratic Athens led the Delian League whereas Sparta , an oligarchy , led the Peloponnesian League . Both leagues were a loose and changing coalition between many city states ~ see related links below for additional information regarding both the Delian and Peloponnesian Leagues .
the power struggle between Athens and Sparta. Athens had emerged as a dominant naval power in the Aegean while Sparta was the leader of the Peloponnesian League. Tensions between the two city-states grew as they competed for influence and resources, eventually leading to the outbreak of the war.
. . . the Peloponnesian War .
Athens and Spartans
Rivalry between Athens and its empire and the Peloponnesian League led by Sparta.
A collision between Athens and its empire and the Peloponnesian League led by Sparta.
Rivalry between Athens and its empire and the Peloponnesian League led by Sparta.
The Peloponnesian War was a conflict between the two city-states of Athens and Sparta .
Rising tensions between the Peloponnesian League led by Sparta and the Athenian Empire which was pushing them too far in Athens' over-aggresive policies.Athens, having turned the alliance against the Persian Empire into an empire of its own, interfered in the other cities to extend its influence. The Peloponnesian League led by Sparta, some of whose members were targeted by Athens, gave an ultimatum for this interference to cease. Athens persisted and war ensued.The fear of the growing strength of Athens.
Rising tensions between the Peloponnesian League led by Sparta and the Athenian Empire which was pushing them too far in Athens' over-aggresive policies.Athens, having turned the alliance against the Persian Empire into an empire of its own, interfered in the other cities to extend its influence. The Peloponnesian League led by Sparta, some of whose members were targeted by Athens, gave an ultimatum for this interference to cease. Athens persisted and war ensued.The fear of the growing strength of Athens.