The Spartans, having led the successful resistance to thePersian invasion 480-479 BCE, wanted to bring the Greeks whosettled in Asia Minor, and were under Persian rule, to mainlandGreece, in order to avoid the problems which had brought on thewar. The Athenians wanted to bring these cities under protection,and organised the Delian League of 180 city-states to give mutualprotection.The Spartans, with their own internal problems of serfuprisings, withdrew, giving the leadership to Athens. Both remainedfriends, and twenty years later the Athenians sent a force to helpSparta suppress a serf revolt. This went wrong when the Athenianforce started to sympathise with the serfs, and the Spartans sentthem home. Ten years later when the Persians agreed to peace,relations between Sparta and Athens went from bad to worse, and asAthens tried to misuse the Delian League to promote its owninterests and prosperity, this resulted in the disastrousPeloponnesian War between Athens and the empire it had created outof the Delian League, and the Peloponnesian League led bySparta.