Another newbe question...

[Karacan]

First comes movement through magical means (teleportation spells, faery trod, etc).
Then comes friendly movement, that means moving from one province into a friendly one.
Only then comes enemy movement. That means you can't catch a retreating army in the province he was before. Unless you magic something.

If armies are small enough, there's a chance that they will pass each other, too. I think that has to do with province (like, there can be bigger armies passing each other in the forest than in the plains), too, but I can't remember if I read that somewhere or thought to myself how cool that would be.