Whilst continuing with his mission to dominate Prussia and the east of Europe, Napoleon was also deeply embroiled in a war in Spain. France fought both Portugal, Spain and Britain in what is known as the Peninsula War; Britain was an ally of Spain, and got involved when the latter was invaded. The Duke of Wellington first distinguished himself in Spain, where he commanded the British Army. The Spanish army consisted of irregular, swiftly-moving units who used their superior knowledge of the terrain to fight off the larger French forces: it is from these fighters that we get the term guerilla warfare. In fact, Tolstoy's is one of the earliest known uses of this word. The Peninsula War was also the inspiration for the Spanish artist Francisco Goya's great series The Disasters of War.