Most of the regions of the elven domains weren't anything of note, mostly being regular forests and the likes, as such, there wasn't much that they could do against the onslaught of dirt-bloods.
They could only throw everything they had at the invaders in a desperate bid to defend their homeland… But fortunately for them, the elusive leader of the elves spoke a decree, and all elves living in regions that could not be properly defended would either be sent regions that could be defended as reinforcement, of be brought to the heart of the elven domain, at the feet of the legendary tree grown by the very first ruler of the elven domain.
As a result, although the dirt-bloods gained lots of territory in one fell swoop, they didn't actually weaken the forces of the elves in the least, only occupying regions who had been abandoned by its inhabitants.