The article analyzes the complex relations among the Third International, its national section in Mexico, and the Nicaraguan anti-imperialist movement led by Augusto C. Sandino, in order to inquire into the causes of the breakdown of the alliance. Practically unknown Comintern documents safeguarded in Moscow, as well as Sandino’s correspondence kept in Mexican archives, make it possible to recover the little known history of the relations within the “triangle” formed by Sandino, the left, and the Mexican government in the second half of the 1920s. By showing that one of the reasons for the communists’ interest in Sandino was broadening their influence through frontist tactics, the article reviews those relations and explains the causes of the break-up between the Comintern and the Sandino movement. The paper concludes that Moscow and the Mexican communists were unable to maintain an adequate level of interaction with Sandino and that personal conflicts exacerbated the situation.