There's currently no way to actually move an army around (wars are event driven). It's in the works though.
Oh okay, so how am I supposed to conquer and win wars?
Have a high martial (gives extra levies) lead the host focus, hire mercs, pray that you win battles 😂then siege target.
How do I hire mercs?
Should be one of the actions under deeds when at war
Found it - Managed to get to Emperor
New patch is in - you can raise hosts now.
