[merlinme]

As examples of how not to do it, though, both Rome: Total War and Heroes of Might and Magic used to drive me slightly nuts the way they would recalculate the route without telling you, if they bumped into an enemy unit. Sometimes you want them to do something else; sometimes you want them to attack. What you almost never want to happen is for them to spend five turns moving on difficult terrain around the blocking army. Yes you can stop them if you realise, but I've quite often got them to continue movement without thinking about it, and wasted a turn or two. Or, to take another example, in Hearts of Iron 2, if a province changes hands, you'll actually end up attacking unexpectedly, and that's almost never what you want.

There is an equivalent problem in Dominions 3 when a province changes hands, which is why I raised it.