The Spanish Peninsular War (1808–1814), which saw open confrontation between the Spanish people together with their British and Portuguese allies against Napoleon, was more than just a war of occupation and national liberation. Remembered for its violence and drama, it was unusual given that two countries who had traditionally been allies, France and Spain, entered into armed conflict without their governments declaring war. Histories and memoirs drafted since then in France, England or Spain show clear bias in their interpretations, hence the difficulty in finding reliable information to draft a rigorous analysis of those historic events. However, two centuries having elapsed since the start of this conflict allow us to address the topic today with greater objectivity. At the start of the war, the climate in London was favorable to cooperation with Spain. Yet the feeling of failure soon took hold of British society due to having embarked in another long and costly war, and many felt disappointment with the scarce cooperation of Spanish troops. However, among the few who defended the importance of the Spanish cause were the Wellesley brothers, the 'British Gracchi', who together maintained this fragile alliance between both countries until the final victory over the French. Richard, the eldest brother and Minister of Foreign Affairs for the United Kingdom, changed the war against France and was decisive in the success on the Iberian Peninsula. Beside him, his younger brother Henry coordinated official relations between Britain and Spain in his role as ambassador plenipotentiary in Cádiz, maintaining a climate of collaboration up to the end of the war. But the efforts of the two brothers would not have borne fruit without the intervention of a third, Arthur Wellesley (Duke of Wellington), who, in a five-year campaign defeated the French troops which outnumbered his, liberating Portugal and Spain from Napoleon’s grip. The same man who in 1815 commanded one of the allied armies which came together to defeat Napoleon at Waterloo. Based on original sources, this book aims to clarify the setting in which these important events for the history of Spain unraveled, through the study of anglo-hispanic relations during the years of conflict.