This work explores the characteristics of the nineteenth-century Peruvian Army, prior to the Pacific War (1879-1883). It argues that the nineteenth-century army was a weak institution, product of the consolidation of a military culture in the first half of the century, expressed in a series of war related practices. This military culture obstructed all attempts of reform during the economic growth cycle of the guano boom (1845-1874) and was the one practiced by the Peruvian Army during their defeat in the Pacific War (1879-1883).