An analysis of the immediate causes of Peronism in its formative stages is included in this study of the emergence of powerful pressure groups and the decay of traditional political parties in Argentina during the period 1930-1946. A detailed, well-documented description of Argentine politics through four administrations. Originally published in Spanish as Partidos y poder en la Argentina Moderna (1930-1946) by Editiorial Universitaria de Buenos Aires in 1966.