There are at least two ways to answer this question. One way is to argue that Regeneration is not an anti-war novel. First, because the work is historical fiction, we might assert that it was necessary for Barker to include Sassoon's protest against the war as an important facet of his character, but that his protest is not central to the novel. Second, as the narrator does not play an intrusive role in the story, there is no overarching judgment of the occurrences and events that carries a didactic anti-war tone. Third, in the characters' observations there is most definitely a condemnation of well known pacifists like Bertrand Russell and Ottoline Morrell. Finally, we may argue that Regeneration is not an anti-war novel because it contains no discussion or evaluation of the aims and purposes of war; it only deals with the effects of war, and therefore cannot be said to be firmly positioned in one camp or the other.
There seems, however, to be more evidence supporting the position that Regeneration is an anti-war novel. Barker offers realistic detail of many horrible war scenes, dwelling upon the destruction that war wreaks upon men's minds. These details comprise a large portion of the novel. Furthermore, Sassoon, the novel's hero, rejects all justification for such a high amount of human suffering. Barker presents Sassoon as a likable, sympathetic character who is perfectly clear and reasonable; it seems natural for us to accept his judgments as sound. Perhaps most important, the protagonist of the novel, Rivers, ends up questioning his traditional belief in duty at all costs. Yealland does his duty to "cure" patients, but clearly the physical and emotional cost of his alleged cure is too high. Rivers cannot help concluding that the complete control over human lives, which is brought to the extreme in wartime, is harmful to everyone.