Ivar the Blood-hand is a Gaunt-lord, a being of great and dark power, made in mockery of the Wizard Radagast the Brown. He is weakened at the moment, not only by his meddling with Radagast, but also as he continues to raise his army of Dead within the bounds of Garth Agarwen.
Ivar the Blood-hand must fall. His strength must fade, and he must become what he should have been all along: a memory of a bygone age. His strength is born of raising the Dead and returning those that have fallen back to battle.
This is his role, and stopping him from achieving this role, no matter how minutely, will see that the mark of his hand is removed from the land. To do this, you must ensure that his banners remain so that at his death his power is split between them.