Ah, here we get into my Illuminated Traveller setting. The Droyne on Andory managed to restart the Ancients "network", a commincation and information storage device that operates on the Jump 23 dimension. One side effect is that sensistives are drawn towards the general area. The restart happened near the end of the Long Night, bringing the Aslan and (future) Sword Worlders across the Great Rift. The Zhodani detected the emissions, and saw them as a threat, stopping expansion into the Marches because of it.