The Impenetrable Hinterland

The vast majority of Tria's western continent is known as the Impenetrable Hinterland: territory known for its extreme hostility towards any permanent settlements or excursions within its borders. Waves of attacks from monstrous flora and fauna prevented the initial Feln colonists from exploring any deeper than its coasts during their occupation of the planet and after some generations they stopped trying as it became too costly to pursue.
  Since the FTPR regained control of Tria, they began funding their own excursions into the Hinterland. Although still met with significant natural hostility and a high failure rate, the Ministry of Industry felt that the losses were notably less than those faced by the Feln and that the economic potential of the Hinterland may be worth the high cost involved in taming it. The Ministry of Trian Heritage, which also had an archaeological interest in the Hinterland, partnered with the Ministry of Industry to begin funding permanent outposts in the Hinterland. Major corporate entities were also encouraged to invest in the colonies and, after roughly 80 years, the project has painstakingly carved out the network of inland settlements and coastal cities that we see in the present day.