You heard it here first folks, with the Aetherium Crown you can have your own undead army.
Step 1: Read the Aetherium Wars book, you can find said book at either the Dawnguard or Vampire castles. It also spawns randomly in dungeons and whatnot.
Step 2: Complete the quest
Step 3: CHOOSE THE CROWN! It allows you to select two standing stones at once.
Step 4: Get the Ritual Stone as your standing stone.
Step 5: Hot key both the Ritual Stone and the Aetherium Crown
Now use the Ritual Stone power, this raises undead around you to fight for you for 3 minutes.
Go into your hot key menu and take off the crown, and put it back on. Then re-select the Ritual Stone power.
Rinse and repeat.
Couple of pointers though, try to find a limit. When your army is lagging your console, stop there.
Every 2 minutes, stop your army. And wait an hour, when they all die just bring them back to life.
Stay away from Quest NPC's as they cannot die. And your entire army will attack that one NPC forever.
If this happens, defeat the NPC, and while their regaining their health, leave the area.
Fast traveling will severely reduce your undead numbers, or completely destroy it.
Now go to every major city, and take over Skyrim!