I feel like armies should have to spend a turn in preparation for a field battle, as battle camps were a thing. this would allow for allied (or enemy) reinforcements to actually come and support you in a fight if they're nearby. It would also allow for an opportunistic 3rd enemy to attack two armies and cause a 3-way battle.
To clarify, how this would work is everyone would make their moves like normal on the campaign map, but instead of the battle immediately taking place, it would occur after all the pieces had moved. then the engagements would take place. I actually think this is how the game worked with Shogun 1 and Medieval 1 when you were using actual pieces on a board. I feel this version would allow for allies and reinforcements to be a lot more useful.
Obviously this needs to be adjusted for things like ambush battles and such - I really thing they need to remove attacking-ambush battles personally... I just want to have more battles with more factions involved in them than just two.
A brave man marches into danger and ignores his fear. A courageous man marches into danger while embracing his fear.
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Veteran of the Total War franchise since Shogun: Total war. (I was 10)