The Empire spilled out of the portal in a wave, moving forward in a coordinated block through the passage near Stormhaven. Outside of the mountain, the forces of the worldly nations stood against them, resolute but rent by their own differences. Gaps formed in their lines as foes stood apart from each others, eyeing each other warily, and into these holes the corrupted Empire charged like arrows. Their swords rent armor and flesh and bone, and their silent stoicism shook the hearts of their foes.
But even as they moved forward, strange wounds began to appear on their bodies. Their skin warped and tore, and a thick viscous black ichor spilled to the ground. The weight of the World was, seemingly, inimical to their existence here and it wounded them more surely than the swords of the disparate nations. Hollow voices cried out in pain, and the Empire fell back, leaving holes through which the battered defenders could advance.
And advance they did. They poured into the Nether once again, driving the Empire before them. Though their wounds slowed them, the Empire fought with a striking ferocity, giving ground only grudgingly against greater numbers until, at last, they were pushed back into the very portal they had spawned from.
And it was here that they vanished, again, somewhere else entirely leaving the defenders of the World bewildered. Try as they might, they could not enter the portal as the Empire had, and there were few clues as to where it led.
The Empire had returned. They were defeated, for now, but had always been canny foes. If they could not succeed in their unknowable goals by brute force, inevitably they would try again through more duplicitous means. The wiser nations would keep watch for their inevitable return, while the foolish ones would fall to their black blades.