This information is known ICly only to those familiar with Remba or Kitezh history. Please check +lores for either culture.
Roughly 800 years before game start, the warriors of Kitezh sailed into the waters of Rebma. It seemed like paradise to them. The schools of fish were so thick a man could scoop his shield through the water and eat for a week. The whales were larger than five longships, and showed no fear of sailors. It was almost as if the seas were cultivated, but the early explorers could find no settlements, no people on the surface. Clearly, it was a gift from the gods.
Then, after more and more ships began to enter the rich waters, the strikes came. From beneath the water, strange half-men and creatures with crushing tentacles began to attack and sink ships. The explorers fought back, but their strategies seemed to be predicted, and each battle was decided individually.
The skirmishes wore on for weeks, until both sides drew back, the horror of their losses dawning on them. The Rebmans were losing their nobility at a shocking rate, and the Kitezhka realized that their warriors, drowned in the sea, were too far down to see the rising sun.
There was no formal end to the war; both sides merely recoiled in shock and ceased hostilities. The explorers returned to their home waters, and the Rebmans did not pursue. Many generations later, after Kitezh settled its hostilities with Amber, Rebma offered an official end to the war as a gesture of good faith. These days, the two nations merely raid inside each other's borders, like neighbors do.