The Valle de Los Caídos (constructed 1940–59) is an enormous Spanish Civil War memorial complex just north of Madrid. It consists of a gigantic basilica with an underground crypt set on a granite hill adorned with colossal sculptures. The memorial park extends over a large hilly area of woodlands dominated by a giant cross and contains 40,000 graves of both Nationalist and Republican fallen. Built by General Franco, it was intended to be conciliatory, but the complex is a controversial celebration of the Catholic Church and conservative nationalist values. Since a memorial to Republican values was never feasible, Picasso's well-known painting Guernica (1937) effectively became the alternative memorial. Commissioned by the Spanish Republican government, then engaged in a protracted defense against an insurgency led by Franco, Picasso painted it for the Spanish Pavilion at the World Fair, Paris, 1937. The massive work—over twenty-five feet wide (7.76 meters)—that has become a major icon of twentieth-century painting was painted very quickly when Picasso read news in the Paris press of the bombing of the Basque town of Guernica by German bombers on 26 April 1937, one of the earliest raids on a civilian population and a direct forerunner of the mass bombings of World War II. When the Republican government fell in 1939, Picasso's Guernica was already on tour in Europe; it had been shown in London twice, once at the New Burlington Gallery in the West End and then in the following year, 1939, at the Whitechapel Art Gallery in the East End at an exhibition opened by Labor leader Clement Attlee. The painting ended up back in Paris, but with a war imminent it was sent to the United States, eventually entering the collection of the Museum of Modern Art, New York. Because it was a commission from the Republican government and Picasso had been paid, the artist designated it the possession of the Spanish people and ruled that the canvas would not be returned to Spain until liberty and democracy had been restored. The painting eventually went back in 1981.

By the time the painting was touring Europe in 1938–39, it had already become a generalized symbol of opposition to war. While it was in New York, Guernica became a site for protests against the Vietnam War. When the Whitechapel Art Gallery, London, reopened in 2009 after a refurbishment, a full-size tapestry replica was installed by the artist Goshka Macuga. The tapestry was owned by the family of Nelson Rockefeller and on loan to the United Nations in New York, where it hung in the corridor outside the Security Council. When it was shown at the Whitechapel, it was hung in front of a blue backcloth recalling the incident when UN officials covered the tapestry in 2003 as US Secretary of State Colin Powell made his address to the UN Security Council in support of the invasion of Iraq. When the exhibition Conscience and Conflict: British Artists and the Spanish Civil War opened at the Pallant House Gallery, Chichester, in 2014, a textile recreation of Guernica stitched by artists and activists in a series of workshops in public locations was shown alongside the exhibition to affirm the continuing relevance of its themes to contemporary experiences of war and infringements on human rights.

Support for the Republican cause in the Spanish Civil War galvanized a European-wide community of artists producing an outpouring of works of art, posters, prints, photographs, literature, and poetry responding to the urgency of the situation. Some artists volunteered for the International Brigades; many were involved in fund-raising and protests in support of the Spanish Republic. There is a substantial literature on art and the Spanish Civil War, especially in Germany, which contributed the largest numbers of volunteers to the International Brigades, mostly in exile from Hitler's fascism. There are also many texts on individual works of art related to the war, especially Picasso's Guernica, which has given rise to a numerous monographs and scholarly articles, as well as works such as the American David Smith's Medals for Dishonor (1937–40). To date there has not been a survey of British artists' responses to the crisis, although the Artists International Association, which many artists supporting the Spanish Republic's cause joined and which organized British artistic opposition to war and fascism, has been well documented. Simon Martin's Conscience and Conflict is a well-illustrated record of the exhibition held at Pallant House, and, with its footnotes and bibliography, it also functions as reference work for the period.

Following the sections of exhibition, the book raises questions about cultural heritage under threat, the Artists International Association, poster campaigns, British surrealist works on the Spanish Civil War, and the influence of Guernica. It has a useful chapter on artists who supported the Nationalist cause, who are not often discussed. Particular questions about whether being an activist was distinct from being an artist and questions about the value of political art are raised alongside the overarching concern that the rise of fascism threatened to make it impossible to be a modern artist. Among the artists and photographers, women including Felicia Browne and Felicity Ashbee are extensively discussed. Essentially functioning as an extended comment to the exhibition, this publication is a useful documentation of the exhibition, but that is also its limitation. Numerous questions are raised and many sources and lines of inquiry are thrown up, but there is little analysis; connections are not made between different issues, and the book comes to no particular conclusion. It is, however, extensively illustrated, and its primary value rests in providing an excellent starting point for further research into the question of British artists' reactions to the Spanish Civil War.