Plague / Epidemic
While the young Aelgari Empire kept crime away by developing the Order of the Naia Caeli and making things a lot safer, trade became a lot more profitable. Sadly that trade helped spread a terrible plague.
This horrible plague eliminated a lot of the population, and without a general populace to farm the land, expansion seemed like the only other option. The Empire exploded outward, taking over large swaths of land and trade was not encouraged as much. The main source of income became taxes and the goods stolen when ravaging new territories. This new policy formed partially because of the great fear of plagues, and after the lessening of trade there was no plague as crippling as the Red Sickness. This made the Aelgari Empire much more like the militaristic expansionist empire it is today. In the meantime, scores of merchants, farmers, nobles and fighters succumbed to the horrible plague.