With a favorable climate, plentiful marble, and very fertile land, many nations owe part of their success to Dion's friendly nature. Food was plentiful, and much aid was given to other nations to secure alliances and keep feisty neighbors (especially Sadah) off their backs. Sculpture and architecture flourished, and the implementation of a series of aqueducts provided fresh water to outer cities in the nation.
Land, however, was not what Dion was most notable for. They were a seafaring folk, and were the first to discover lands far away from Ozel. It's believed that some Dionese have ancestry to some sort of ocean-dwelling race, given the slight webbing in their hands and feet, but nowadays this trait offers little extra benefit.
Dion's actual landscape is comprised of mostly wetlands and dense temperate rainforest. Rain is near-constant, but with it comes fertile soil and areas rich with chemical, herbal, and mineral resources.
It's believed that the Empire invaded Dion out of necessity, as the previous conquests had taken a toll on its supply resources. That being said, it's no question that they probably would've attacked sooner or later. The capitol city of Troriraxos was taken over in 821 GWE.