World War I (1914) massively disrupted the publishing industry. The shortage of paper increased production costs significantly, even as demand for reading material increased, particularly with the armed forces. Quality suffered even as large quantities of literature were produced. The trade in Germany was initially able to survive the way but suffered in the chaos of post-war inflation. Paper supplies in Britain returned to normal very quickly after the war but the roaring market for books that had been thriving beforehand saw a steep reduction in sales. The European middle class lost of lot of their disposable income in the high tax depression that followed the war. Publishers who tried to continue targeting the educated consumer market struggled to survive and most quickly closed down.
A new social enterprise quickly became popular in post-war Britain. The book club, whose member purchase the same book and discuss the themes and plot at (typically) monthly meetings. Publishers were not particular fans of the book club's popularity at first, as mass purchases often influenced the "bestseller" list, which then impacted sales. However, the book club brought welcome business and drew people away from borrowing books at libraries. This had increased enormously and struck a blow to book sales. Unfortunately, the book club fell into decline in the 950s with the introduction of cheap paperbacks into supermarkets and outlets outside of the bookshop.
The collapse of the stock market (1929) in America had an impact on trades worldwide. The sale of British books in the USA hit rock bottom and the publishing industry internationally suffered. In an effort to keep customers and attract new ones, The Sunday Times launched an annual book exhibition in London. Publishers spent a lot of money on newspaper advertising and coupons. The Great Depression did not prevent the publishing industry's evolution. In 1935, Allen Lane launched the distinctly recognisable Penguin paperback series. This new series was extremely popular. At a sixpence per copy, they remarkable value for money.