[Taqwus]

Aye, normally when you see devils in an indy province it indicates one or more Soul Contracts. It could however have been set by the .map file, however.

If you're dealing with a mess of indy devils -- well, they're not going anywhere, and if it's a Soul Contract they'll gain one per turn. That's slow enough that with the right equipment you may be able to attrit them -- a lightning-immune air mage providing storms, wrathful skies, perhaps tossing some orb lightning or summons briefly then fleeing for instance. Storms will ground the devils (bring a staff, don't wait to cast this!), so they'll stick around the ground-pounders burning them up for longer and won't be able to insta-kill you.

More generally applicable, perhaps, is that (unless set by the map file...) these devils are units, not commanders. Kill all the leaders first with assassins or spells (and indies never have protective domes, and most types aren't astrally proficient) and the devils will rout instantly since indies won't have province-defense commanders to help.