What do you think about adding a counter-attack option/card?

The goal is to draw an opponent in thinking he can attack a weakly defended territory, only to receive an immediate counterpunch.

The idea would be to let you put armies in a territory that is off the frontlines. The card would allow the player to specify that the armies should automatically counter-attack when an opponent successfully attacks an adjacent territory.

You could take this idea further with multi-attack: Once the counterattack succeeds, let the surviving portion of counterattacking army proceed to attack the territory from which the opponent's attack was initiated.

I'm sure there are many ways to improve or extend the basic idea, but you get the picture.