Ernest Hemingway traveled to Madrid in March of 1937 to observe the Spanish Civil war firsthand. He reported on the war for the North American Newspaper Alliance. In March 1937, he traveled to Madrid to observe conditions firsthand. His observations and experiences provide the inspiration for the novel.
The Spanish Civil War lasted from July 1936 - March 1939. To give a brief summary, the war was fought between the Loyalists who were defending the current Government against the Nationalists or "fascists" (as Hemingway referred to them) which were supported by Benito Mussolini and Adolf Hitler and were led by General Francisco Franco.
Hemingway sympathized with the loyalists as is evident in this novel. One of the main examples of this is the protagonist, Robert Jordan who fights on the side of the loyalists against Franco's "fascist" forces. Another example is Robert Jordan's love interest, Maria who was raped and orphaned by the fascist regime.
The following are events that actually happened and are referenced in the novel:
- Segovia Offensive This actual event took place between May 31 thru June 6, 1937. Hemingway describes Robert Jordan being assigned to blow up a bridge during an attack on the city of Segovia.
- Battle of Guadalajara The loyalists defeated the Italian and Nationalist forces. This battle took place between March 8 thru March 23, 1937. Hemingway uses this actual battle as an element in shaping the character of Robert Jordan. Jordan claims that he follows the loyalists due to their discipline at Guadalajara.
- Aerial bombings The two most notable aerial bombings during the Spanish Civil war are the bombing of Guernica and the bombing of Barcelona. The bombing of Guernica took place on April 26, 1937. The bombing of Barcelona took place between March 16 thru March 18, 1938. The protagonist, Robert Jordan is constantly anxious due to the appearance of enemy planes that are continually in the vicinity.
- Firearm malfunctions There is a famous photograph of Hemingway demonstrating how to operate a firearm to an actual member of the loyalist army when his firearm malfunctions. Robert Jordan is described as shooting an enemy horseman while the surrounding camp attempts to arm themselves with a machine gun that did not even "come with directions."

The events at Ronda This is a somewhat controversial topic. Whether or not what Hemingway describes in the novel actually took place is debatable. I am only including it in this list due to the fact that there was an actual uprising in 1936 that took place in the south, but historians still are unable to pinpoint exactly where or exactly what occurred during this uprising. Some sources speculate that some 7,000 priests, monks and nuns were slaughtered while their churches burned while others speculate that Hemingway's depiction of events is accurate. Hemingway describes this in detail in Chapter 10 of the novel. He describes 500 people who are allegedly fascist sympathizers being thrown off of a cliff side from a house. Hemingway himself even has conflicting quotes regarding this event. He tells his friend A.E. Hotchner:
When Pilar remembers back to what happened in their village when the
fascists came, that's Ronda, and the details of the town are exact.
However, in a 1954 letter to his friend Bernard Berenson, Hemingway admitted to completely fabricating the scene.
The most significant part of the novel is the bridge that Robert Jordan is planning to blow up. The bridge and the planning of its demise is the central plot to the novel. There has never been any definitive proof that the bridge in the novel was real. Hemingway never spoke of the bridge being an actual bridge. Literary scholars maintain that the bridge is simply used as a metaphor.