Napoleon's strategic error in Spain was categorical: he assumed Spanish national resistance would follow the pattern of other European states he had defeated—that a military victory at the top would produce political compliance below. Spain was not a state in the Westphalian sense. It was a fragmented political culture where loyalty to village, province, and Church vastly exceeded loyalty to whatever government sat in Madrid.

The Guerrilla System

The Spanish word guerrilla—'little war'—entered European military vocabulary from this conflict. Spanish irregular forces imposed a constant drain on French occupation forces: French columns might lose 10% of their strength to ambush over 100 kilometers without ever engaging an enemy formation. By 1812, approximately 300,000 French troops were in Spain, most pinned in garrisons or convoy escort. These men were not at Borodino.

Wellington and Torres Vedras

Wellington's Anglo-Portuguese army gave Spanish resistance a conventional anchor guerrillas alone could not provide. When the French massed sufficient force to drive him, Wellington retreated behind the Lines of Torres Vedras—a fortified defensive system outside Lisbon that the French, whose supply system could not sustain a siege, could not breach. He waited, bled, and counterattacked when French strength ebbed.

The Drain

In 1812, Napoleon pulled substantial forces from Spain for his Russian campaign—a decision that critically weakened both theaters simultaneously. He never had enough men in either place. Spain was not the cause of Napoleon's downfall; it was the precondition that made other causes fatal.