Religious event
After the gods sealed the remains of the great evil, they still had many things to rebuild from the war. It was in this situation they felt that many of their followers were dying in the Savage Isles. As they rushed there to find them fighting among themselves, they set out to restore peace but failed to do so.
When the gods once again arrived in the Savage Isles to get the situation under control and restore peace, many missionaries rejected them as trickery by their rivals. Furthermore, those communities they managed to convince quickly found themselves unable to compete with their local rivals as the rivals did not care much for respecting the new peaceful ways of their neighbours and still wanted revenge for their grudges.