Slitherine

In my MP game, I defeated my opponent in battle and his army retreated a region. In that region he now had his main army (the 5th) and a very small army (the 18th). My main army targeted the enemy 5th, and I ordered "motivate troops" in order to deliver the coup de grace. My human opponent merged the larger army into the smaller army because it had a better general and ordered the combined army, the 18th, to move to another region adjacent to my army. During the turn resolution my main army moved to where the enemy 5th army used to be and then halted. Had I targeted the 18th then the planned battle would have occurred in the region to the west.

I am sure that my human opponent didn't do it on purpose, but it saved his bacon. It would be nice if when a targeted enemy army merges into another enemy army that my army acquires the merged enemy army as the new target. From the example above, my army should have switched targets to the enemy 18th and pursued them.

I wonder if you can do a similar trick if you split your army and then merge the rest of the first army into the second, thus renaming the army, and side-stepping into another region to avoid battle.

That's not how it works, you don't actually target an army, but a unit within the army you target. So if your opponent does some reshuffling, no one can predict if you will pursue army, A, B, C ... You'll pursue the army that contains the unit your army targeted, and no one can know which one. So it's all about probabilities here.

OK, good to know. I don't understand how he evaded my attack then when his two armies merged into one and side-stepped me. By they way, when you target an army, the game tells you which army that you are targeting; not unit.

Yes, the game does not want you to know which unit you are actually targeting, it is telling you the container of the unit, thus the army.