The publishing house kept working intensely even during the First World War, mainly on the publication of magazines for the troops on the front such as La Tradotta, which included contributions from famous illustrators and writers such as Soffici, De Chirico and Carrà.
In 1919 the publishing house headquarters were transferred to Milan. After the First World War, Mondadori launched several successful book series including Gialli Mondadori in 1929, the first example of an Italian book series dedicated to detective and crime novels, by international writers, a new genre for Italy. The series is distinguished by the yellow (giallo in Italian) color of the covers. The response from the public was positive, with five thousand copies sold in a month and eight thousand after a hundred days. In addition to those who are considered the masters of the genre, such as Raymond Chandler, Dashiell Hammett, Georges Simenon, Agatha Christie and Erle Stanley Gardner, in 1931 even some Italian writers began to take an interest in the genre and write yellow novels.
In 1960 Mondadori launched Il Club degli Editori, the first Italian mail-order book club and in 1965 became the first Italian publishing house to launch low-cost paperbacks for sale through newsstands (Oscar Mondadori), an experiment that would be a huge success and that was imitated by many publishers. The aim of the series was to reach an audience not used to buying in bookshops. The first novel published was A Farewell to Arms by Ernest Hemingway, who immediately experienced great results in terms of copies sold.
Between 1950 and 1965, the number of employees at Mondadori rose from 335 to 3,000 and resulted in the company's decision to construct a new building in the outskirts of Milan, specifically within the municipality of Segrate.
In 1968, Giorgio Mondadori, Arnoldo's son and chairman of the publishing house, decided to assign the project for the new headquarters to Brazilian architect Oscar Niemeyer, after having admired his work on the Foreign Ministry (Palácio Itamaraty) in Brasilia three years earlier. Construction began in 1971 and the new headquarters was inaugurated in January 1975.
Mondadori was one of the first Italian publishers to enter the e-book market and in 2000 an agreement was signed with Microsoft Corporation for the creation of the first Italian site for the sale of electronic books. In 2010 Mondadori accelerated its presence: in June, the Group’s online bookstore launched a store dedicated to digital books, with a vast catalogue of titles in Italian and English. In December, Mondadori reached an agreement for the international distribution of books produced by the Group’s publishing houses on Google Books and Google eBooks.
The digital development continued in July 2011 with an agreement between Mondadori and Amazon that makes the Group's e-books available through the Kindle store. In September 2011, Mondadori's digital titles were also made available on the iBookstore for the Apple iPad, iPhone and iPod touch. The following year Mondadori Group and Kobo Inc., a leading company globally in digital reading, signed an accord for the distribution in Italy of Kobo's eReading platform and related devices. In 2014 Mondadori bought the trademark and assets of aNobii, the global social reading platform with more than a million users around the world, of which around 300,000 in Italy, with the aim of supporting the process of growth in digital for books.
According to en.wikipedia.org