Peninsular War (1808–1814): Napoleon’s Campaigns in Spain and Portugal

The story of the Peninsular War doesn’t begin with cannons and drums, but with the ambitions of one man — Napoleon Bonaparte. By the end of 1807, he already controlled most of Europe and set his sights on crushing his old enemy, Britain. To strangle the island nation economically, he ordered all continental countries to stop trading

British commander Arthur Wellesley overseeing the removal of the French flag after his forces retook Ciudad Rodrigo, Spain, in 1812, during the Peninsular War.

Napoleon sent his troops there — under the pretext of “protection,” but in reality, he occupied the country. Spain, formally an ally of France, allowed the French to pass through its territory, unaware that it too was walking into a trap. When French soldiers began taking over Spanish fortresses, the people erupted in fury. In May 1808, Madrid rose in rebellion — bloody, spontaneous, and desperate.

It was from these street battles that the Peninsular War began. France now faced not just armies, but entire nations fighting for their freedom with whatever means they had at their disposal. Soon, Britain came to Spain’s aid. What Napoleon had thought would be a “small campaign” turned into a long, exhausting war — one that would reveal the first cracks in his empire.

Key Battles and Campaigns

When the gunfire in Madrid finally fell silent, Napoleon realized things had taken an unexpected turn. Spain and Portugal had become a true nightmare for the French army. It all began in 1808, when the Spanish insurgents achieved a shocking victory at Bailén — the first major surrender of French forces since the Revolutionary Wars. The defeat struck a blow to Napoleon’s prestige, and he personally crossed into the Pyrenees to restore control. By the end of that same year, his armies had retaken Madrid — but the victory was short-lived.

While the French struggled to crush the uprisings, British forces under the command of Arthur Wellesley — the future Duke of Wellington — were already operating in Portugal. Their first mission was to protect Lisbon and halt the French at the borders. Between 1809 and 1810, the French invaded Portugal three times, but each attempt failed. Wellington turned the country into a fortress: in the north, he built the famous Lines of Torres Vedras — a network of defenses stretching nearly 80 kilometers. When Marshal Masséna’s troops arrived, they faced an impenetrable barrier. Hunger, disease, and relentless guerrilla attacks forced the French to retreat.

Battle of Bailén, 1808

By 1811, the fighting had shifted deep into Spain. The French still held major cities — Madrid, Seville, Zaragoza — but beyond their walls, power belonged to the rebels. Every mountain pass, every bridge, every village became a battleground for ambushes and surprise attacks. The Spanish guerrilla — a people’s war — wore down the French far more than any formal battle ever could.

In 1812, Wellington went on the offensive. His army, strengthened by Spanish and Portuguese allies, achieved a brilliant victory at Salamanca. The French abandoned Madrid, and for the first time in years, the people of the capital welcomed their allies as liberators. Napoleon, preoccupied with his impending invasion of Russia, couldn’t send reinforcements — and the situation in the Pyrenees became disastrous.

In 1813, the decisive battle took place at Vitoria. The army of Joseph Bonaparte, Napoleon’s brother, was crushed, losing its entire baggage train and artillery. The remnants of the French forces retreated across the Pyrenees. The final clashes occurred in the spring of 1814, after the fall of Paris itself. At the Battle of Toulouse, the French fought with their old determination, but the outcome was already sealed: the Peninsular War had ended in the empire’s defeat.

This campaign became one of the bloodiest and most exhausting for France. The war lasted six years, claimed hundreds of thousands of lives, and proved that even the strongest army in Europe could be bogged down in a struggle against a people fighting not for a throne, but for their homeland.

Guerrilla Warfare and Resistance

While regular armies fought on maps and open fields, the true power of the Peninsular War lay hidden in the mountains, valleys, and villages. The Spaniards and Portuguese, deprived of resources and centralized command, created a new kind of warfare — a people’s war. It was during this time that the word guerrilla, meaning “little war,” first appeared. But in reality, it was anything but little.

The guerrillas wore no uniforms, received no pay, but knew every hill and every trail by heart. They ambushed supply convoys, cut communication lines, wiped out messengers, freed prisoners — and vanished before the French could strike back. It was a war without front lines, where any peasant could be an enemy, and every forest a trap. French officers, trained for discipline and open-field battles, suddenly faced chaos — a kind of warfare where it was impossible to tell friend from foe, soldier from civilian.

The birth of guerrilla warfare.

Across Spain, dozens of guerrilla bands operated — some becoming legendary. One of them was led by Espoz y Mina, the famous Basque commander who organized entire “people’s armies” that held the French at bay in the northwest. In Andalusia, the fighters of Juan Martín, known as El Empecinado, terrorized French garrisons, forcing them to keep large forces behind the front lines. Even women joined the resistance — carrying weapons, delivering messages, and rescuing the wounded.

The guerrillas couldn’t win the war on their own, but they were the reason Napoleon’s victory became impossible. Every burned bridge, every destroyed convoy drained the emperor’s army bit by bit. The French commanders tried to fight this “invisible enemy” through terror — mass executions, village burnings, and food confiscations. Yet these brutal measures only deepened the hatred and strengthened the unity of the local population.

In Portugal, the situation was much the same. When Wellington built the Lines of Torres Vedras, the guerrillas aided the British with intelligence, supplies, and swift raids. They confused the French, creating the illusion that a vast army was moving against them.

For Napoleon, the Peninsular War was the first time imperial might collided with the will of the people. French marshals complained that “every stone on the Spanish road shoots.” And indeed, the guerrilla became a symbol of an unbroken spirit. In the years that followed, the Spanish experience served as an example for national liberation movements across Europe and even beyond.

Britain and the Allied Forces

When France invaded the Iberian Peninsula, Britain saw an opportunity to strike at Napoleon without engaging him directly on the continent. London had long maintained strong trade ties with Portugal and knew that if the French seized its ports, the route to the Atlantic would be cut off. So, in the summer of 1808, British troops landed on the Portuguese coast under the command of a young but determined general — Arthur Wellesley, the man who would soon become the Duke of Wellington.

At first, the British army was small and acted with caution. But early victories — at Roliça and Vimeiro — proved that the French could be stopped. After these successes, Wellesley restored Portugal to allied control and soon turned it into a fortress. His strategy was simple yet brilliant: avoid hopeless battles, rely on naval support, and wear down the enemy slowly, step by step.

Wellington planning defense lines at Torres Vedras

When Marshal Masséna invaded Portugal in 1810, Wellington had already completed the Lines of Torres Vedras — a formidable system of fortifications shielding Lisbon. The French advanced, but behind every village they left losses to guerrilla attacks, hunger, and disease. In the end, they were forced to retreat, leaving thousands of bodies scattered along the road.

Britain didn’t act alone. Its allies were the Spanish juntas and local armies — disorganized but burning with the desire for revenge. Coordinating them was no easy task: Spanish commanders often distrusted the British, and discipline among their troops was weak. Yet Wellington showed remarkable flexibility — he respected the Spaniards’ pride, relied on their knowledge of the terrain, and built effective cooperation with the guerrillas.

Britain’s naval supremacy played a crucial role. Supplies and reinforcements arrived steadily across the Atlantic, while the French communication lines stretched over the Pyrenees — long and vulnerable. Moreover, the British had money: they financed the Spanish resistance and kept the allied armies equipped with food and weapons.

Gradually, the tide began to turn. By 1812, the allies had taken the offensive: Wellington captured Ciudad Rodrigo and Badajoz, then crushed the French at Salamanca. His army marched into Madrid, where the people welcomed him as a hero.

The British intervention became the turning point of the entire campaign. Without it, Spain might not have withstood the pressure, and Napoleon could have maintained his grip on the Pyrenees. Instead, the Peninsular War turned into the stage where the empire began to crack — and Wellington emerged as a symbol of perseverance and strategic patience, the man who managed to defeat the greatest army in Europe.

Defeat and Consequences of the Peninsular War

By the time the last French soldiers crossed the Pyrenees in 1814, Napoleon was already on the brink of collapse. The Peninsular War — which he had once dismissed as a minor conflict — turned out to be one of the most devastating for his empire. It lasted six long years, drained France’s resources, and crippled its war machine from within.

The main reason for Napoleon’s defeat was his failure to grasp the strength of popular resistance. In Spain and Portugal, he faced not just armies, but entire nations ready to fight to the end. The French soldiers controlled the cities, but beyond their walls ruled the guerrilla — an invisible war that destroyed convoys, severed communications, and sapped the army’s morale. Every step forward came at a heavy price, and every “victory” brought losses that could never be replaced.

French troops retreat through the snowy Pyrenees, tattered flags, weary soldiers helping the wounded.

No less significant was Britain’s intervention. Wellington turned the Iberian Peninsula into a theater where the French army lost the initiative for the first time. His defensive strategy, masterful logistics, naval support, and alliance with local insurgents made the British forces a decisive power. The victories at Salamanca and Vitoria shattered the French administrative system and forced Joseph Bonaparte to flee from Madrid.

For Spain and Portugal, the war was both a trial and a rebirth. After the expulsion of the French, Spain restored the Bourbon dynasty, and in 1812, amid the struggle, the juntas adopted the liberal Cádiz Constitution — a symbol of the nation’s yearning for freedom and new ideals. Portugal preserved its independence and slowly began to recover from the devastation.

For France, the Peninsular campaign became a black hole that swallowed tens of thousands of soldiers and vast resources. Napoleon, having diverted some of his best corps there, weakened his position before the looming invasion of Russia. Many historians believe that the Peninsular War marked the beginning of the end for his empire — a slow but inevitable collapse of a system built on endless conquest.

In a broader sense, the conflict reshaped the European continent. It served as a lesson for future generations — showing that the strength of the people and the spirit of national resistance could overcome even the mightiest army in the world. From the ashes of the Peninsular War emerged a new understanding of freedom, patriotism, and independence — values that would define the 19th century.