It has been 60 years since the humans invaded. It is still not clear why they came, other than to fight their enemy, but who that enemy is has never been ascertained.
The humans have finally sent an envoy to the native races explaining why they invaded a few generations back. Their world was conquered by an outsider race, and their race enslaved for centuries. A revolution eventually overthrew the outsiders, and they were driven from the human world. The aftermath, however, left their world mostly scarred and broken.
A human expedition was able to track the outsiders through their portal back to this world. It was decided that humanity would return the outsider’s favor, and conquer their world. They did not expect to find other races, and so eventually after decades of war, it was decided to make peace it was decided to make peace. Now the humans have finally discovered the origin point of the outsiders. The lake island in the middle of the continent. The humans intend to march on the island, but have requested assistance in scouting the island first.