Where, then, can lie the snare?
Your theory presupposes an impassable barrier to arrest the French when they are deep in the country and an overwhelming force to cut off their retreat when that barrier is reached.

The overwhelming force does not exist and cannot be manufactured; as for the barrier, no barrier that it lies within human power to construct lies beyond French power to over-stride." "I should not make too sure of that," Samoval warned him.

"And you have overlooked something." The major glanced at the Count sharply and without satisfaction.

He accounted himself--trained as he had been under the very eye of the great Emperor--of some force in strategy and tactics, a player too well versed in the game to overlook the possible moves of an opponent.
"Ha!" he said, with the ghost of a sneer.

"For instance, Monsieur le Comte ?" "The overwhelming force exists," said Samoval.
"Where is it then?
Whence has it been created?
If you refer to the united British and Portuguese troops, you will be good enough to bear in mind that they will be retreating before the Prince.