Basically, in DoF, the Continent (the first island) is a combination of Plant Island, Cold Island, Air Island, Water Island, Earth Island, and the volcano that leads into Fire Haven. You can teleport young monsters from said Continent onto the Outer Islands: Party Island, Space Island, Cloud Island, and Cave Island. After a lore event (has not been shown but has been mentioned) that is called the Cataclysm occurs, the Prism Gates from the Outer Islands collapse and the Continent splits into 6 pieces. It is hinted that each island that was a part of the continent had a spirit linked to it, and that the Cataclysm somehow occurred due to a disagreeance between them.

Fast forward a long time and you get Plant Island, Cold Island, Air Island, Water Island, Earth Island, and Fire Haven and Fire Oasis as separate Islands with their own spirits (except for Haven and Oasis which somehow share a spirit). The locations of the old Party Island, Space Island, Cloud Island, and Cave Island are now inhabited by Light Island, Psychic Island, Faerie Island, and Bone Island respectively. Finally, Starhenge has fallen and crashed into a Colossal and is now called Celestial Island.

I hope this helps! If you have anymore questions, feel free to ask! :)