The David Kilcullen Collection (merged thread)

[Ken White]

But a road without troops to patrol it only lends mobility to the enemy. As Foust points out, the Romans learned this to their chagrin.

There are no absolutes other than getting killed if you screw up too badly. Every action seeks an equal and opposite counter reaction; the key is to anticipate that, plan accordingly and be prepared to adapt.

None of which negates the fact that one most usually does not have all the troops available one would like -- that's always been generally true and is unlikely to change -- and thus, one must have alternatives.

As for the Romans, to include the Kilcullen and Foust citations, there's always only so much one can do with troop constraints -- and, far more immutably, the terrain and people of a place.