Between 1925 and 1929 he lived in Nicaragua and dedicated himself to the local syndicalism activism of laborioust tendency. He urged the affiliation of the Nicaraguan Worker's Federation ("Federación Obrera Nicaragüense") to the Panamerican Worker's Central ("Central Obrera Panamericana"), which was affiliated to the American Federation of Labor. In this time, he married Carmela Castrillo and had two children, Carmelita de la Selva Castrillo (1925-1931) and Salomón de la Selva Castrillo (1927). His daughter Carmelita was born whilst de la Selva served as the director of newspaper "Nicaragua Libre" of the Nicaraguan Patriotic League and perished in the earthquake which shook Managua on March 31, 1931. By 1930 he had published articles supporting Augusto César Sandino published in San José, Costa Rica through different media such as the "Diario de Costa Rica" and "Repertorio Americano" of Joaquín García Monge. and in 1935 he moved to Mexico City, where he was able to influence Mexican politics; along with his brother Rogelio de la Selva, he was advisor to President Miguel Alemán Valdés. In 1933, a son of de la Selva's, Juan, is born in Panama to actress Betty Schroeder. Whilst in France, as a Nicaraguan ambassador for the Government of President Luis Anastasio Somoza, he died on February 5, 1959 in Paris.