In the summer of 1938 Klaus Mann travelled together with his sister Erika to Spain. The civil war seemed almost lost to the Republican Army at this time. In April 1938, the fascists had broken through to the Mediterranean and had divided the Republican territory. Bolstered by the temporary lifting of the French arms embargo, the Republicans were making preparations for the Ebro offensive, the last major counter-offensive, when the Mann siblings arrived on 23 June.

Klaus Mann undertook his trip as a correspondent of the Pariser Tageszeitung. From 2 July to 11 August he published a series of articles entitled Aus dem Spanischen Tagebuch (From the Spanish diary). Erika Mann wrote for the Neue Volkszeitung, New York. They also wrote articles for Swiss newspapers.

Klaus Mann interviewed the Spanish Foreign Minister Alvarez del Vayo, reported on his impressions in Barcelona, Valencia and Madrid, and wrote about his experiences and encounters on the Ebro front, in a military school and a children's home. The journey was marked not only by lasting and deep impressions, but also by night-time bombing raids and moments of danger that - as revealed in his diary - had a much deeper effect on Klaus Mann than on his sister Erika. The siblings left Spain on 14 July 1938 after a three-week stay.