Complex sentence: Most of Arcadia, Corinth, Argos and the Argolid succumbed to him or joined him and the Achaeans were routed at the Battle of Dyme.
Split into simpler sentences: Most of Arcadia, Corinth, Argos and the Argolid succumbed to him or joined him. Finally, the Achaeans were routed at the Battle of Dyme.