I believe he was referring to the 19th/
early 20th centuries concepts of "forts,"
i.e. Maginot Lines which are fixed and
don''t allow for maneuvering.
The Ukrainian "defensive" line is
neither fixed nor do they lack the
ability to shift forces as needed.
The Ukrainian army seems to be
very mobile. Its Kharkov offensive
followed by its maneuver to
defend the Donbas farther south
shows that.
Sometimes as what was famously
said, "Retreat hell. We're advancing
in another direction."
His thoughts also extended to the strategy of a defensive stance. Sometimes this cannot be avoided.
It goes thus. If you want to fire a shell, or a missile, you must manufacture that shell and or missile.
Once fired, you must manufacture replacements in order to continue the fight.
Russia will have little trouble in this area. a few scattered reports of sabotage aside, their military industrial complex remains in the top tier of its blue book value.
In any campaign, the targeting of such resources is way up there on the target priority list. You can bet Russia has been on this mission from first blood. This was made evident by their occupation of Chernobyl, what would be Ukrainian nuclear production, if any.
At this time, Ukrainian military industry is likely a hot mess of broken and burning misfit toys. The advantage is to the Russians for their ability to replenish their ordnance.
Without Ukraine adopting a primarily offensive stance, pushing into Russia to break their toys, this will be a growing disparity of force.
Russia need only make sure the Ukrainian broken things stay that way while applying modest pressure until their remaining war fighting material dries up.
About the only liability in an offensive stance is over-extension. Men and material get spread out over too many fronts to maintain them.
As we cast a gaze to Nicaragua, I'm pretty sure they can handle at least a three front war. So far they have just one, setting up for a second.
