i'll pitch my 2 cents in here before Athens gets to much of a bashing, for me i think the Corinthians played a big part there quarrel with Corcyra over Epidamnus and then the formentation of rebellion in Potidea ( a tribute paying vassal of Athens ) lays the blame at there door, you can't blame Athens for having an Empire and the supression of revolts within that Empire as for Corcyra they had a perfectly legimate right to seek a defensive alliance with the Athenians when pressed on by the Corinthians, even though the Corcyrans had defeated the Corinthians in a naval engagement at Actium they knew the weight the Corinthians held in the Peloponnesian leauge and the forces they could harness for a counter offensive so it is perfectly logical for them to go to the Athenians who were the counter balance to the Peloponnesians.
As for the Spartans in a legal sense there decision to support the Corinthians and the Potideans was in relation to the treaty with Athens illegal, i shall explain this as follows the treaty declared that so long as a polis was neither alligned with the Peloponnesian bloc or the Athenians then they were perfectly entitled to pursue a treaty, Corcyra having a treaty with neither Athens or Sparta was acting legitimatly in going to the Athenians to safeguard there intrest in Epidamnus. My personal opinion was that when the Spartans called the league together concerning Potidea they allowed themselves to talked into war by not only the Megarans but also the Corinthians who were acting totally out of there own intrest this being one they had a grudge against the Corcyrans for being a former colony who didn't pay the respect the Corinthians believed they deserved and two the fact that Potidea was another former colony who had fallen under the influence of the Athenians go figure
