This seems to be an occurrence that happens mostly early in the war before divisions and corps are allowed but has always confused me.
One example. I was railing in reinforcements to Beauregard at Manassas at the same time McDowell entered the region. McDowell;s large Army managed to engage ONLY the small group group of reinforcements on route in the same region to Beauregard's Army, thus annihilating them. Beauregard's large Army just sat there idly and never engaged.
Is there a rule which decides what separate stack will be attacked in a region with multiple stacks? How was McDowell able to engage only one separate stack and not the other ( both of my stacks were on D stance)? I've also seen the A.I attack the same region with multiple independent stacks early in the war which made for some confusing battles, any information on this would be awesome thank you.