Looking back, I should have mentioned that the reason I suggested some mountain traveling ability/skill was to give more variety and depth to the game by having factions with more distinct or unique abilities.
Mountain bandits might have the ability to travel through mountains (although at a slower rate than on open territory) and if our friendly warparty acquires a mountaineering skill, we might add have a tactical disadvantage of some sort if we're attacked in the mountains.
Forest bandits could travel through forests with no slowdown and/or have increased combat effectiveness in a forested area. For simplicity, this effectiveness might be represented by adding a little more hit damage to their attacks.
River Pirates combat abilities - both movement/damage - might be increased by being closer to their natural haunts: river areas. Their increased confidence in fighting near their home turf could be represented in faster battlemap speed and/or increasing their battle damage ability slightly. River pirate's ability to cross rivers anywhere would be cool.
And so on, for each faction. I'm not talking about huge increases in abilities and for some - maybe most - it would be too slight for most of us to recognize it most of the time. However, for close fights or outnumbered fights, that margin of effectiveness could be the difference between destroying the enemy bandits or breaking off the attack and calling it even.
Anyway, my main point is that each faction should have some ability that relates to the area they're fighting in and traveling through. Like Sea Raiders spawning off the coast and appearing in ships (represented by some longboat icon), that sort of thing.
I've mentioned these thoughts before, but I believe I've not gathered these ideas in one place.