How did the peloponnesian war mark an important turning point in greek politics?

The Peloponnesian war marked a radical turning point in Greek politics. Before 403 BC, Athens had a dominant relationship with its allies, which included small island cities around the empire. These cities took advantage of Athens' maritime protection. However, after the war, instability started to prevail as many of these cities started scrambling for supremacy and creating independent empires of their own. However all these empires were short-lived.