THE THREE FALLS
The first fall was of the Enacki, roughly seven thousand years ago a full third of their number rebelled against the plan to give their planet to one of their "children"--young races whose evolution was altered and accelerated by the Enacki--when they went to the next plane of evolution.
 
The second fall was of the Menuhim, one and a half thousand years ago. Roughly a fifth decided to follow the ideals of the Zantrophe.
 
The third fall was of the hybrids, eight years before Incursion begins.