Dark Elve's are born warriors, they spend all their time raiding other's and fighting eachother.
They Have a better leader (Malekith) and use incredibely powerfull chaos magic which the High Elves are to scared to use.

They seem to attack Ulthuan pretty regualrily and always do alot of damage.
(They would have won last time but for Teclis)

Most of the High Elf forces are Militia, and are completely out classed by the Dark Elves.

So how come Dark Elves haven't just destroyed them?