A region in unrest recovers from its source outward. Spread ends only when the source's Trust is back at 55%, and a full Food store brings it there fastest.
The spread ends when the source recovers, and its paused growth effects return. Once no Settlement in the region is in unrest, the extra enemy pressure ends; enemy groups already on the ground stay until they are cleared. Slow recovery usually means the stock is no longer full or the Food went to a different Settlement.
A region that is repeatedly dragged down by a neighbour can protect itself with a Civil Defense Office.