Sounds like the standard Chaos campaign. Takes forever. You've already completed the hard part (taking Norsca) so the rest is just slowly grinding down the old world.
Eh, not really. You can do it in about two to four hours (based on loading times) on pretty much any difficulty, unmodded.
Sort-of-powergaming strategy for the WoC campaign:
This is all with a single stack. Lightning strike is also critical for this. Archaon kinda sucks for this because he has no monsters or artillery to instantly assault cities. Skip Norsca, it's a waste of time and it allows for the AI to build up their forces. I usually just force-march past Kraka Drak (it's not worth it taking them on, since they are hard bastards to crack) and go straight south near Erengrad (sp?). Raze a few targets and head into the Empire. Don't bother taking capitals unless they are undefended or you've already pretty much completed your army comp. Also, leave the Vampires alone, they'll take advantage of your rampage to go for Karl's throat. If they don't, make sure you do since it's part of your wincon.
Once the Empire main faction is down, go straight for Bretonnia. One weird thing I noticed is that if you are far enough away (and Bretonnia apparently is far enough away), Sarthorael bugs out and, instead of making a straight line to kill you, he just starts attacking whatever imperials are left. Defeating big bird is not necessary to win, so let him pretend he is important. Once the Bretonnia faction is down, just go southwards taking out the Bretonnian dukedoms, Tilea, Estalia and maybe orcs until you hit the short wincon. If you are going for the long victory, forget the humans and head for Karaz-a-Karak instead.
Mind you, I actually have fun powergaming in this game, so your mileage may vary.