A stack inside the structure-location of the region must first exit the structure to be able to exit the region.
If you drag-n-drop the stack into a different region this will occur automatically. Conversely you can drag-n-drop the stack out of the structure-location and into the field of the region and then drag-n-drop it into a target. The results should be the same.
From what I understand, your opponent is targeting Grant's stack to move to a region north of the Ohio, and each time when it exits the structure-location it is attacked by the besieging force.
This can be happening from a number of different reasons:
- Grant's stack is in OP (Offensive Posture), which means it will attempt to attack any enemy forces it encounters during the move (which is probably not the case here, but... )
- The Union has <5% MC (Military Control) in the region and Grant's stack is in DP (Defensive Posture), in which case it will automatically change to OP with the same results as 1. .
- Grant's stack is in DP or PP but the besieging force is in OP, in which case every time Grant's stack leaves the structure-location the besieging force will attempt--and more than likely succeed--to attack Grant's stack.
Once a stack has been involved in a battle its movement orders are generally canceled, and unless it retreats it will remain in the region, so to exit the region the goal is to not engage in battle the turn the stack is to exit the region.
One can achieve this in a number of ways.
- Since there is a harbor controlled by the side attempting to leave the region in the region one could load the stack onto transports--drag-n-drop the land stack onto the transport's stack--and sail out of the region. If the besieging force has achieved entrenchment level >=3 and it has the Bombard Passing Ships SO (Special Orders) button pressed, this could be very costly to the transports and their embarked troops unless there are a lot of ironclad and gunboats to soak off most of the bombardment.
- If there were no harbor or no actual transports available one can still use the RivTP (Riverine Transport Pool) to move the escaping stack directly into a neighboring river region and then either sail away or simply land across the Ohio. I don't think the moving stack will be subject to attack by the besieging force in this case--unless it assaults--but I'm not 100% sure and in any case they will still be subject to Bombardment.
- Durk has already mentioned simply attempting to avoid combat. One thing to note is that the difference between DP and PP is that PP gives you an advantage at retreating from battle at the cost of greater losses compared to DP.
- The last possibility that I can think of would be to offer the 'sacrificial lamb'. Depending on the size of Grant's force one might break out a large brigade or even a division and leave it in the region in DP without orders to move. In this case the besieger might attack the 'sacrificial lamb' instead of the escaping stack, in which case they escape.
- One might actually raise the stakes and attack with the 'sacrificial lamb', which would increase the chances that the besieger is engaged in battle which the escaping force retreats.
- One last possibility, which I think Gray Fox came up with would be to break the escaping force into its constituent units, put them all into PP with the ECSO(Evade Combat Special Order) and hope the most of them get out.
- One might also combine 6. with the 'sacrificial lamb' ploy.
One further note, if a force attempting to move across a rive is engaged in battle while still moving across the river it will be handled basically the same is if they were moving across the river INTO the region. In other words they will be subject to invasion penalties. This is because, although logically forces would be traversing the river in smaller forces the game assumes that they are all moving at once in one big group. So if the stack is already 'in the river' it must return to fight.
Good luck to your opponent. He's going to need it.