Imagine Japan, ten times the size – that’s where you’re at. Part of the what you learn is the “Old Empire” of Aquitaine, that fell close to a hundred years ago. The mainland is (by all accounts and rumor) a wasteland inhabited by all sorts of badness and ruins from a cataclysm that occurred close to a thousand years ago.
Dion is a city and kingdom that was one of the old provinces of Aquitaine (on a map of Japan look for the city of Osaka, that’s where Dion is). Aquitaine itself covered the whole of the island and was founded by refugees from the mainland in the aftermath of the aforementioned cataclysm who united the island under one rule. Notable neighboring kingdoms are Vasconia (near to Kobe), Navarre (near where Kyoto would be), and Morin (near Nagoya). These are far from the only kingdoms and only major cities, though Dion is ranked the third greatest, distant Taormin the second, and Navarre the greatest (and the former capitol of Aquitaine).
Because of the overall hostile nature of the mainland, plus the very intricately interwoven cultures of the island of Aquitaine, the various guilds of that old empire have pretty much survived intact and have actually prospered in the aftermath of the empires fall as they operate across the borders of the various kingdoms and act an excellent counterweight to attempts to reform the empire – despite some factionalism. Similarly, many of the more illegal guilds have also retained control over their respective domains. The Old Faith, the En Khoda Theos Kirk, and the Society of Light still exist, but it is worth noting that the veneration of the Great Gods seems absent for the most part – while the worship of the various Godlings has increased greatly.