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You can also leave the men here as guards or local militia. They will not like that very much (resulting in a morale drop), and you will still have to pay them for the week. However, this is the only way to get militia/guards into rural, badlands or townsland regions.
Is it still true that the only way to get militia into rural, badlands, and towns-lands is by dropping your unit?
This used to be the case, I believe, but I think this is no longer the case, as Gustav says.
Sounds like the disband page.