Peninsular War

The Peninsular War (1807–1814) was a war between the First French Empire under Napoleon and the Spanish Empire for control of Spain and Portugal. 
In the beginning, France and Spain were allies. The war began when French and Spanish armies together invaded and occupied Portugal in 1807. 
It became more serious in 1808, when France and its ally Spain came into disagreement, and became enemies. France attacked and invaded Spain, and Napoleon made his brother Joseph Bonaparte its king. General Sir Arthur Wellesley, later Arthur Wellesley, 1st Duke of Wellington, became famous in the war. The war lasted until certain European states joined together in the Sixth Coalition and defeated Napoleon in 1814, invading Southern France as far north as Toulouse.
The word "guerilla", which means "little war" in Spanish, was first used in 1808, when guerrilla warfare was used by the Spanish against the larger and better armed regular French Army.