Complex sentence: Humans and Orcs were forced to flee the western continent of Chantra and under the leadership of Ugdrasil, the Orcs colonised a small part of the continent where they began the re-building process.
Split into simpler sentences: Humans and Orcs were forced to flee the western continent of Chantra. Under the leadership of Ugdrasil, the Orcs colonised a small part of the continent where they began the re-building process.