It is more realistic to be able to retreat a battle. Sitting on quick retreat should be able to do some trick. But this needs to be implemented carefully. Sending out an army is a costy thing. Need to have a balance to prevent discouraging attacks.
The biggest problem of Thardferr in the means of battle dynamics is "instant attacks". Always everytime even it is a mere platoon or a huge army, they just pop up without the defender kingdom noticing. That is hardly manageable. Kingdoms not watching over thier borders deserve to perish.
Didn't give this too much thought yet but if possible it should go like this in basic: Launch an attack, wait for army to reach the destination (should be able to change things or even abort), within a reasonable time defender gets a notice they are being attacked. Adjust their strat or army. Then battle happens.
I know that means writing a whole new battle mechanics. But, that is what thardferr is lacking.