Children of the Sun, Children of the Moon

From the introduction:

In millennia past, Travelers left the kingdoms of Sun and Moon to explore the land. They founded fiefs on their travels and many of them settled in these places, taking rule over the native stars. In time however, those Travelers who journeyed the furthest found a force beyond the known. An unrelenting power of destruction. A crushing monstrosity that opposed all the good that the Travelers could do. Many fell to that power and many more were tainted. They retreated to their domains but the infection of hatred and desire for destruction slowly corrupted them so that once noble rulers became despots. Valorous warriors became beasts. Loving explorers turned to heartless conquerors.