Help. Five stacks of Bjorlings decided to ignore whole of badlands and border princes and march straight for my totally unprotected Wissenland. I send two stacks south to deal with them, but they caught me on the march and I lost big battle. Volkmar is chasing Beastmen in Wasteland, which they burnt to the ground when I wasn't looking. That leaves Karl Franz completely alone against this tide of darkness...
I'm thinking about making a tactical retreat to Reikland...
personally I'd move karl to talabein and wait for chaos to attack me. A full army + garrison can beat all those armies. the main reason is that there is a hard limit of 40 units for the same faction. Your army + garisson should be almost 40 units. The chaos warriors will assault your walls with the same numbers, any extra unit they have will only appear when you either kill or shatter their in battle units.
Now the concrete battleplan: as the empire you have a lot of ranged troops, these will be devastating to chaos troops since they will not have a direct counter.
First you want to direct your towers at their siege towers, get as many as you can; then you focus on the hellcanon (you just need to destroy it, ignore the crew after that) then you focus on chosen then any other strong unit that is big enough to be easily hit by the towers (focus giants, chaos warriors, chaos knights while mostly ignoring chariots, trolls, chaos spawn ).
Second you want your best melee infantry where the enemy doesn't have siege towers, even chosen with great weapons will have a hard time beating halberdiers when climbing the wall with ladders. Your archers (preferably hand gunners) will be above the gates (one unit front and one unit back) the rest of the wall should be mostly melee infantry.
thirdly ,and the most important part, make a "kill box" near each gate, the AI will always use their cavalry, chariots and monster infantry once they open their gates, as such make a square with your halberdiers (they have anti large and charge defense against large) and ranged troops behind them (outriders are excellent for this), these ranged troops must not fire on the enemy group engaging the halberdiers that are protecting them, instead directing fire on the enemy units that have their backs turned. Because cavalry, chariots and monster infantry units have very few models your ranged fire should make short work of them.
fourth, keep reserves , that reinforce any weakened part. If karl has deathclaw you can use him on the walls weakening strong troops and preserving your walls infantry.
Some more tips:
remember to withdraw from the walls if it is not worth fighting over it (towers are controlled by chaos, your group(s) is losing the fight and no reinforcements can arrive in the mean time), don't mind sacrificing 3-5 groups on the walls if it means that you can protect your kill box /town center better.
If the enemy starts breaching your kill box try to withdraw to near your control point; by bringing all your units together + karl franz leadership bonus might just be enough to outlast the chaos attack.
The enemy will flee if it loses their leaders + losing they start "to feel" they will lose the battle, even if mostly your units are borderline routing.
Kholek and archaeon are a pain, there is really not much you can do about them; focus fire on them if you have line of sight (artillery is really good against kholek). Remember to not over commit troops against them (like have more the 1 unit of a melee infantry fighting against them).