Upon release it received rather positive reviews; it won the Somerset Maugham Prize in 1962 and during the following few years was translated and published in Portugal, France, Germany, Denmark and Italy.

Fairly rare critical remarks claim that the work is about storytelling rather than historical analysis, that some interpretations advanced are doubtful, and that some sources are trusted too much while other have not been consulted at all.

Afterwards in Francoist Spain numerous books went to print, but they largely adhered to propagandistic format; the best and the most detailed one was also plagued by censorship limitations (Joaquín Arrarás, 1940–1943).

Beyond Spain there were merely numerous highly personal accounts (e.g. Julió Álvarez del Vayo 1940),[5] partisan party narratives (e.g. Herbert Matthews 1958)[6] or works which focused on some particular dimensions of the war (e.g. Patricia van der Esch 1951,[7] David Cattell 1954[8]).

The Cambridge graduate, former employee of the Foreign Office and member of the British delegation to the UN Disarmament Commission, he was released at his own request due to unease with the policies he was asked to promote.

[20] Some publicity given to his clash with the Foreign Office made him an attractive catch for the Labour Party; he unsuccessfully stood as parliamentary candidate in 1957-1958 for Ruislip and Northwood.

[22] Some sources claim that in 1955 Thomas visited Spain for the first time and began his research on the civil war,[23] yet in his Introduction, dwelling on origins of the book, he did not mention such an episode.

Thomas shared the outline also with his agent at Eyre and Spottiswoode (the British company which published The World Game), Douglas Jerrold, an active supporter of Franco 20 years before.

By the autumn Thomas cashed in the $300 advance from Harper Brothers and £250 from Eyre and Spottiswoode,[31] both considerable amounts (in 1957 average annual earnings in the UK were some £390, the Ford Anglia model cost £571).

He did research some documents of the Foreign Office, available at the time, the League of Nations papers in Geneva and numerous printed collections of American, German and Italian diplomatic sources.

Others included e.g. Pablo Azcárate, Alberto Onaindia, Josep Maria Tarradellas, José María Gil Robles, cardenal Ángel Herrera, Manuel Fal Conde and Don Juan de Borbón.

[38] Thomas also engaged in epistolographic exchange with a number of individuals, including war correspondents like Herbert Matthews and Henry Buckley.

[46] Initially the British edition on its cover was to feature the notorious photograph of Robert Capa, allegedly presenting a Republican militiaman in a moment when hit by enemy bullet,[47] but eventually the publisher settled for simple text, with no graphics.

[58] Jay Allen was irritated by Thomas, "terribly fuzzy about a lot of things",[59] while Southworth dismissed him as the ethically dubious one who "does not want to take sides", a writer but not a historian.

[63] Similarly, Arnold Lunn, who wrote to the conservative Catholic Herald, saw the narrative as somewhat biased in favour of the Republicans and underlined reported prejudices of the author against Franco, yet he still thought the work highly readable and interesting.

[64] The Sphere acknowledged the book as notable historiographic achievement, especially that "Hugh Thomas admits his sympathies are with the Republicans but this does not prevent him from being scrupulously fair to the Rebels".

[65] The Illustrated London News published a large, one-page review by Charles Petrie, who during the war co-led a pro-Nationalist propaganda campaign in Britain; though somewhat cautious and with reservations, the article nevertheless recommended the book as a sound piece of historiography.

[70] Norman Padelford[71] claimed that "the volume gives the fullest and quite the most insightful account of what transpired within Republican circles" but "is somewhat less definitive on the Nationalist side".

[72] Stanley G. Payne praised level of detail and "emotional disengagement", but complained about insufficient archival research, "rather poor organisation", "clumsy style and confusing syntax".

[78] In 1960, shortly before the publication, Thomas enjoyed brief attention of Spanish press; many titles referred his letter to The New Statesman, where he withdrew earlier reservations (expressed in 1958 review of the work by Herbert Matthews) as to authenticity of Moscardó’s phone talk with his son during the siege of Alcazár.

It was noted that though Thomas was "bien conocido por su inclinación izquierdista",[79] he behaved like a gentleman and even offered his apologies to Moscardó's widow.

The first translation – anonymous and later criticized for manipulating the original[94] - was into Spanish by the Paris-based émigré publishing house Ruedo Ibérico, released already in 1961 (La guerra civil española).

By this time the book has been translated into Swedish (Spanska inbördeskriget),[107] Dutch (De spaanse burgerloog),[108] Russian (Гражданская война в Испании),[109] Japanese (スペイン市民戦争),[110] Chinese (西班牙内战：秩序崩溃与激荡的世界格局，1936-1939)[111] and Hebrew (מלחמת האזרחים בספרד).

[114] Some editions contained appendices, not published in other cases (e.g. the US version of 1986 included one appendix dedicated to Spanish economy, another one focused on the International Brigades, and one more with figures on the Catalan industry production).

One such case, dated 1967, ended up with detention of a Spaniard in question; as the book was among numerous bulletins and leaflets carried, the man was charged with "illegal propaganda" and "spreading communism".

[145] In 1974 Ramón Salas Larrazábal commented favourably that when preparing his work, Hugh Thomas intended to "escribir la primera [historia] con intención de imparcialidad, aunque no saliera perfecta".

[154] According to some history professionals, until today it is "the best general work in English on the Spanish Civil War"[155] and it "stands without rivals as the most balanced and comprehensive book on the subject".

[167] Paul Preston, in popular statements usually highly apologetic towards his academic master, in opinions intended for specialist audience adheres to the cautious tone when noting ambiguously a "highly colourful narrative account" and summarising that the book "did an enormous amount to popularize the subject but it constitutes a readable compendium of information about the war rather than a major historiographical landmark".

[168] Thomas's effort to maintain "liberal objective stance" might be taken against him, with remarks about "merely attempting to find an equilibrium", which reportedly led to initial "dominance of narrative over analysis", merely "corrected somewhat" in subsequent editions.

Before he was a young disarmament activist unknown to wider public, former civil servant with no permanent job, and the author of two failed novels, who kept hovering around left-wing circles.