Humankind: Withdraw From Ongoing Combat

I'd like to see an option to withdraw from active combat added so that every battle isn't a fight to the complete elimination of one side or the other. This would also be a solution to the "army locked by combat" problem that some people have when one of their armies is close to two enemy armies who engage in combat. Here's how I suggest it works:

1. A re-enforcing army or "locked" army can withdraw at any time provided it has not spawned any units into the battle yet. This would cause it to "retreat" across the map just as if it had chosen to retreat when attacked, but without causing any change in war support. If a re-enforcing army has spawned one of its units it loses this option.
2. If an army has spawned any of its units, it can choose to withdraw starting at the beginning of the second turn. It must do this before it has moved or attacked with any units. If you choose to withdraw, your units pass their turn but do not get the +2 strength bonus that passing turn normally gives them. At the beginning of your next combat turn the battle ends in defeat and your army retreats.
3. You cannot withdraw from a siege defense with the exception of re-enforcing armies that haven't spawned units yet. Siege attackers can withdraw normally.
4. Armies with Varangians or Samurai can't withdraw unless the Varangians or Samurai in the army have been eliminated.
5. The AI will attempt to withdraw from battles once the balance of power in the battle reaches the point where it thinks it can no longer win.

I think it might be too difficult to code "retreat zones" given the way the battle mechanics work, but that would be an even better way to do it if it were possible. This way doesn't require any complicated new mechanics to be created for the battle system, however, which is why I tried to keep it relatively simple.