Published between 1828 and 1840, Napier's History of the War in the Peninsula was a tremendously influential, if controversial, work. He had access to many of the participants, or their papers, including French ones. The work was both highly praised and criticised. Although biased, it remains an important eyewitness source.

Published between 1828 and 1840, Napier's History of the War in the Peninsula was a tremendously influential, if controversial, work. Napier had been actively involved in the campaigns, turning to history in peacetime, in part to refute Southey's account of Sir John Moore. The first volume had a mixed reception, getting both high praise and bitter criticism from participants in the wars. He published several works rebutting his critics while producing the later volumes. Because of his obvious lack of impartiality, modern military historians treat the work with caution, but it remains widely read in the many editions and abridgements which were subsequently produced. Volume 1 covers the period from the Treaty of Tilsit in 1807, which ended war on the eastern front and so left Napoleon free to turn his attention to Iberia, to the aftermath of the death of Sir John Moore, Napier's mentor, at Coruña.