This paper will attempt to shed light on the complex process of construction, financing and projection of the Colombian armed forces in Peru. It will first try to understand the mechanism of mobilization, recruitment and training of rank-and-file soldiers in Venezuela and New Granada. Who were the soldiers of the expedition? Were they recruits with a long military experience? Of no less importance is the study of the officers who commanded these troops: who were the military who were chosen to free the ‘brothers of the south’ and why did young military officers, like Antonio José de Sucre and José María Córdova, lead the expeditionary force? At the same time, the liberation of Peru was an important effort made my the Republic of Colombia, both fiscally and in terms of the mobilization and the control of the population to recruit men. It is, therefore, our aim to analyze the political and administrative procedures that allowed the Colombian authorities to project the expeditionary force far from its base. Finally, one might wonder how the previous experience of warfare in Tierra Firme modelled the attitude of the Colombian army in Peru, not just strategically but also in terms of ‘culture of war’.