Well, your story is quite filled with cliches even now. (I mean no harm)
A lot of fantasy stories tell about a single hero, who defeated a tons of enemies alone. This is makes the story is dull and boring, even if the protagonists is a one-sided, empty character. Interesting side characters make a story far more better.
My story advise:
Arlos, a General of XY Kingdom receives coded reports about the neighboring areas is run amok by peasant rebellions, noble civil wars. (First tension)
The king ordered a conviction about it, and the nobles (generals, high priests etc.)
wants to protect their homes against the peasant raff. Arlos, one of this nobles lead his army to the borders and investigate the areas. The army led by our protagonist is fight against some rebel peasants, who entered the place, where Arlos stays with his army. One of their prisoner-in-war told Arlos, that a strange infection killed a lot of people, which lead the total destruction of the ruler system. Arlos gained nothing useful information for it, so he decided, that he takes two-thousand of his men in order to find one rebellious noble and parley with him/her about the events. After entered deeply the areas of the abandoned kingdom, he saw burning houses, killed people. Soon he find a noble, who told him, that the infection caused by a new illness spread by rogue mages. (and of course the healers of that era would not able to fight against, I humbly advise, that you avoid overpowered healers, who resurrect a tons of people)
Well Arlos received proofs about that their king is dead and nobles fought with eachother for the lands. A noble spellcaster (not an Archimonde/Voldemort like) (you the one, who name it or give it gender)
is able to control blood-drinkers any other horrific creatures. (in this universe, it is the only "necromancer")
So this noble collects a lot of undeads. (vampires, ghosts, wights) You Arlos, General of your king found yourself in a land of civil war.
You have some choice:
Pick a side of a noble and help him/she to reclaim the order, or simply slay his/her rivals. You may defeat all of the nobles to conquer the land for your king.
You can be a bloody usurper if you want, you caused rebellion against your king, because you found your king is useless and weak, and he is lead your kingdom to ruin. (It means you wants to conquer two kingdom with your followers). Or you retreat to your borders and wait their attacks.
One thing is sure, the noble who lead the abominations is look for your kingdom as well. You may was an intrical/helpful one, who stood up for one traitor lord/lady and help him/or a defensive one, who just protected his home/or an usurper who stole his king throne and the other kingdom or you captured that land for your king. Whatever way you choose, you have to defeat the rebel noble, who lead the undeads (possibly he/she behind the infection, you decide

)
is a danger for everyone's interests. I hope you like it, sorry for grammar errors.
Oh... and when this is written by me and post it, the full of THIS story about Arlos is full of yours. Only this, no other story created by me, just this is, which written above.
Illusion of Justice, such a great title!