The Peninsular War

British involvement transformed the Spanish uprising from a local rebellion into a major European war. The landing of Sir Arthur Wellesley (later Duke of Wellington) in Portugal in August 1808 provided guerrilla forces with professional military support and secure bases for operations against French forces. This combination of regular and irregular warfare created problems that French generals could not solve.

The Battle of Bailén in July 1808 shattered the myth of French invincibility when General Dupont surrendered an entire army to Spanish forces. This victory, the first major French defeat in Europe, encouraged resistance throughout Spain while demonstrating that French armies could be beaten. The psychological impact extended beyond Spain, encouraging Napoleon's enemies to believe that French power was not invincible.

Napoleon's personal intervention in Spain during late 1808 and early 1809 restored French military fortunes temporarily. His rapid advance to Madrid and decisive victories at Somosierra and other battles demonstrated that French tactical superiority remained intact in conventional warfare. Yet these successes could not solve the fundamental problem of controlling hostile populations across vast territory.

The withdrawal of Napoleon and his best troops for the Austrian campaign of 1809 left Spain under commanders who lacked his strategic vision and political authority. Marshal Soult's invasion of Portugal was repelled by Wellington's defensive tactics, while Marshal Masséna's later offensive failed at the Lines of Torres Vedras. These defeats demonstrated that French forces, stretched thin across multiple theaters, could not maintain the concentrated pressure that had won previous campaigns.