Peninsular War, 1808–14, a conflict fought on the Iberian Peninsula. France was opposed by Britain and Portugal, and by Spanish guerrillas. The war was of strategic importance because unexpectedly heavy resistance required France to divert troops and supplies from other continental campaigns.
France, with the cooperation of Spain, invaded Portugal in 1807. In 1808 a British army landed in Portugal to aid the Portuguese. The French defeated the British in 1809, but later that year British and Portuguese forces, commanded by Sir Arthur Wellesley (who became the Duke of Wellington), pushed the French out of Portugal. Meanwhile, in 1808, Napoleon I put his brother on the Spanish throne; this led to a revolt in Spain, and during 1808–13 Spanish partisans conducted a campaign of guerrilla warfare against the French.
During 1810–11 the British repulsed attacks by large French forces. In 1813 Wellington's forces pushed the French out of Spain. The British had advanced into southern France when Napoleon abdicated in 1814.