This article analyses the organisation of the Army of the Andes, created in Mendoza between 1814 and 1817 with the aim of reconquering Chile from the royalists. The first section studies the role of José de San Martín as an informal arbiter in Bernardo O'Higgins’ dispute with José Miguel Carrera. The aim is to explain why San Martín decided to support O'Higgins, and the immediate consequences of this alliance. The second section addresses the main characteristics of the Army of the Andes and the process of militarisation experienced by the local inhabitants. Everyday life in Mendoza became inseparable from the needs of the revolutionary army. The paper then considers the so-called guerra de zapa and the participation of irregular agents. The involvement of spies and guerrilla officers in the revolution increased as warfare intensified. The final section analyses the crossing of the cordillera by the insurgents and the revolutionary triumph of 12 February 1817 at Chacabuco.
