France and Spain signed a secret agreement to invade Portugal and divide it into separate regions. The treaty gave Napoleon a legal cover to move large French forces across Spain, which soon alarmed Spanish society and leaders. It set the stage for occupation, rebellion, and a much wider war in Iberia.
French and Spanish forces invaded Portugal in November 1807, with General Jean-Andoche Junot leading the main French column. Lisbon fell by the end of the month, and Portugal came under occupation. This occupation helped draw Britain into sustained operations on the peninsula.
By early 1808, French forces were no longer just crossing Spain on the way to Portugal; they were taking key cities and positions. French troops entered Madrid in March, increasing pressure on the Spanish monarchy and public order. This expansion made a break between France and Spain increasingly likely.
On May 2, 1808, people in Madrid rose against French occupation, and the revolt was violently suppressed. Instead of restoring calm, the repression helped trigger uprisings across Spain and a broader war against French control. The event became a turning point from uneasy alliance to open resistance.
In July 1808, a Spanish army defeated a French field force at the Battle of Bailén. It was a major shock because it showed that Napoleon’s armies could be beaten in open battle. The defeat weakened French political control and encouraged wider resistance.
After French setbacks in Portugal, an agreement signed on August 30, 1808 allowed French troops to evacuate Portugal by sea. The convention ended the first French occupation, but fighting soon resumed in new campaigns. It also showed how hard it would be for France to hold territory against local resistance and British support.
Napoleon personally entered Spain with a large army and pushed toward Madrid in late 1808. The city capitulated on December 4, restoring French control in the capital for a time. However, holding Spain required ongoing occupation and constant fighting against regular armies and guerrillas.
In July 1809 at Talavera, British and Spanish forces fought the French in a large set-piece battle. The fighting demonstrated that a combined Allied force could hold its ground against major French attacks. Even without a decisive strategic breakthrough, it helped keep the anti-French coalition alive in Spain.
Wellington ordered secret construction of the Lines of Torres Vedras—forts and barriers designed to protect Lisbon. When Marshal Masséna invaded Portugal in 1810, these defenses helped stop the French advance and forced them into a difficult position without easy supplies. This was a strategic turning point that protected Portugal as an Allied base.
On September 27, 1810, Anglo-Portuguese forces fought the French at Bussaco and repelled attacks on a strong defensive position. Although the Allies later withdrew, the battle contributed to delaying the invasion and pushing the French toward the prepared defenses near Lisbon. It reinforced the idea that France could win battles yet still fail strategically.
On May 16, 1811, Allied forces fought Marshal Soult’s army at Albuera near the key frontier fortress of Badajoz. The battle caused extremely heavy casualties on both sides and ended without a clear decision. It showed how costly control of supply routes and fortresses had become in the Peninsula.
From March 16 to April 6, 1812, Allied forces besieged and captured Badajoz, a major fortress on the Spanish–Portuguese border. Taking it secured a key crossing point and helped protect Portugal from renewed invasion. The siege also became infamous for the severe violence that followed the storming of the city.
On July 22, 1812, Wellington’s army defeated French forces at Salamanca. The win disrupted French control in central Spain and set up an Allied move toward Madrid. It marked a major change from defensive survival to sustained Allied offensives.
On June 21, 1813, Allied armies defeated the French at the Battle of Vitoria. The loss forced King Joseph Bonaparte and French forces to retreat and helped collapse French political control inside Spain. After Vitoria, the fighting increasingly moved toward the Pyrenees and into France.
In December 1813, Napoleon signed the Treaty of Valençay proposing peace and the restoration of Ferdinand VII to the Spanish throne. The agreement reflected France’s weakening position and its desire to end the costly Iberian war. Even so, the military situation continued moving against France as Allied forces pressed into French territory.
On April 10, 1814, Allied forces fought the French at Toulouse in one of the last major battles connected to the Peninsular War. The battle occurred just days after Napoleon’s abdication, and news traveled slowly. It highlighted how the Iberian conflict ended by pushing the fighting across the border into France.
After Napoleon’s fall, commanders on the southwest front agreed to a local armistice on April 17, 1814. This effectively ended the final active operations that grew out of the French invasion and occupation of Iberia. The outcome was clear: France could no longer sustain occupation in Spain and Portugal, and Allied forces had carried the war into France.
Peninsular War: French Invasion and Occupation of Spain and Portugal (1807–1814)