The novel takes place in late May 1937 during the second year of the Spanish Civil War. References made to Valladolid, Segovia, El Escorial and Madrid suggest the novel takes place within the build-up to the Republican attempt to relieve the siege of Madrid.
The earlier battle of Guadalajara and the general chaos and disorder (and, more generally, the doomed cause of Republican Spain) serve as a backdrop to the novel: Robert Jordan notes, for instance, that he follows the Communists because of their superior discipline, an allusion to the split and infighting between anarchist and communist factions on the Republican side.
The famous and pivotal scene described in Chapter 10, in which Pilar describes the execution of various fascist figures in her village is drawn from events that took place in Ronda in 1936. Although Hemingway later claimed (in a 1954 letter to Bernard Berenson) to have completely fabricated the scene, he in fact drew upon the events at Ronda, embellishing the event by imagining an execution line leading up to the cliff face. In Ronda, some 500 people, allegedly fascist sympathisers, were thrown into the surrounding gorge by a mob from a house that faced onto the cliffside.
A number of actual figures that played a role in the Spanish Civil War are also referenced in the book, including:
- Andreu Nin, one of the founders of the Workers' Party of Marxist Unification (POUM), the party mocked by Karkov in Chapter 18.
- Mikhail Koltsov, soviet journalist was the Karkov character in the story
- Indalecio Prieto, one of the leaders of the Republicans, is also mentioned in Chapter 18.
- General José Miaja, in charge of the defense of Madrid in October 1936, and General Vicente Rojo, together with Prieto, are mentioned in Chapter 35
- Dolores Ibárruri, better known as La Pasionaria, is extensively described in Chapter 32.
- Robert Hale Merriman, leader of the American Volunteers in the International Brigades, and his wife Marion, were well known to Hemingway and served possibly as a model for Hemingway's own hero.
- André Marty, a leading French Communist and political officer in the International Brigades, makes a brief but significant appearance in Chapter 42. Hemingway depicts Marty as a vicious intriguer whose paranoia interferes with Republican objectives in the war.