The Peninsular War pits an alliance of Spain, the United Kingdom, and Portugal against France (with some Swiss, German, Italian and Polish soldiers) on the Iberian Peninsula during the Napoleonic Wars.

The war begins when French armies occupy Portugal in 1807 and Spain in 1808 and lasts until the Sixth Coalition defeats Napoleon in 1814.

Spain's liberation struggle marks one of the first national wars and large-scale guerrilla conflicts, from which the English language borrows the word.

Its success is in part decided by the exploits of Spanish guerrilleros and the inability of Napoleon Bonaparte's large armies to pacify the people of Spain.

Throughout the war, British and Portuguese armies defend Portugal and stage diversionary campaigns against French forces while guerrillas bleed the occupiers.

Together, the regular and irregular allied forces prevent Napoleon's marshals from subduing the rebellious Spanish provinces.

French units in Spain, forced to guard their vulnerable supply lines, are always in danger of being cut off and overwhelmed by the partisans, and prove unable to stamp out the Spanish army.

In the final years of war, with France gravely weakened following Napoleon's invasion of Russia, Wellington's allied army pushes across Spain from Portugal, pursuing offensives that bring it past the Pyrenees and liberate the country.

The burden of war destroys the social and economic fabric of Portugal and Spain and ushers in an era of turbulence, instability, and economic crisis.

Devastating civil wars between liberal and absolutist factions, led by officers trained in the Peninsular War, will persist in Iberia until 1850.

The shock of war also leads to the independence of the former Spanish colonies of the Americas and the independence of Brazil from Portugal.