Why could Napoleon beat every army in Europe but not Spain?

THE SHORT ANSWER

• Economic war without an exit. The Continental System hurt Britain (exports slumped, 1808 and 1811-12 were crisis years) but hurt the continent more — and made smuggling a patriotic industry from Lisbon to Riga. Its fatal property: it worked only if total, so every leak (Portugal, the Papal states, eventually Russia) demanded another occupation. A weapon that obliges you to conquer your own allies is pointed at yourself.
• Bayonne: legitimacy fumbled. In Italy or the Rhineland, French rule replaced foreign or feudal rulers and could pose as liberation. In Spain, Napoleon stole the crown of an intact, pious, proud nation by trickery at a conference table. The regime he installed was born illegitimate to every social class at once — and no battlefield victory converts illegitimacy into consent. He later called the Spanish affair the knot that strangled him.
• Insurgency plus sea power. Neither alone sufficed: guerrillas couldn’t take fortresses, Wellington couldn’t hold Spain against 250,000 men. Together — insurgents denying the French their intelligence and forage, the navy feeding Lisbon and Cádiz indefinitely — they created a war the Empire could neither win nor afford to leave. It is the age’s textbook on asymmetric alliance, still on the syllabus.

WHAT IT CHANGED

The veteran drain. Iberia became the Empire’s permanent second front: the men and horses lost there were precisely the professionals missing from the 1812 army, which had to be filled with allied conscripts of doubtful loyalty. Chapter 8’s catastrophe is partly a Spanish invoice.

Nationalism changes sides. Spain proved that the French formula — a people fighting as a nation — worked against France. Prussia’s reformers (Stein, Scharnhorst) rebuilt their state and army on the lesson; the wars of 1813 will be fought by nations, not dynasties, on both sides. The Revolution’s deepest export defeats its exporter.

Cádiz writes the liberal script. The 1812 Constitution — sovereignty of the nation, but a Catholic monarchy — becomes the template for Mediterranean and Latin American liberalism for thirty years; “liberal” itself enters the world’s vocabulary as a Spanish word. When Ferdinand returns and tears it up (1814), he creates the exact grievance the revolutions of 1820 will detonate on.

An empire decapitated across the ocean. With Spain’s king in French custody and its government a besieged junta, Spanish America’s cities face a legal void: to whom is loyalty owed? Their answer — juntas of their own, “conserving” sovereignty — is the door to independence, whatever its authors intend.