At the begining of Jason and Medea's marriage there was peace and harmony. What did Medea do to cause this peace?

In the beginning, Medea helped Jason overcome the odds and capture the Golden Fleece, which belonged to her father. She even went so far as to murder her own brother in order to insure Jason got the fleece he came to Colchis to find. Once back in Jason's homeland, Medea lied to Jason's family, so that Jason could take back the throne usurped by his uncle. Unfortunately, her actions were responsible for Jason's exile from his country.