

Above: The Oscar winning actors from 1943: Paul Lukas, Jennifer Jones, Katina Paxinou, and Charles Coburn.

Basically the most important thing to remember is that just after the monarchy of Alfonso XIII of Spain had been overthrown (1931), there were years of civil unrest in the country between dictator Francisco Franco's Fascists/Nationalists (backed by Nazi Germany) and the leftists/Loyalists/Republicans.
There was such a thing as an International Brigade, made up of volunteers from a number of democratic/anti-fascist countries (including America).
It's interesting to note that by the time the novel and film came out, the war was already over; dictator Francisco Franco and the Fascists already had taken Spain (and remained in control for over 30 years). Today, Spain is a very different country from when the novel and movie came out.
The film is an adaptation of Hemingway's 1939 novel about Spain and the war. I suspect the filmmakers were aiming for the next Gone With the Wind.
In the story, the character of American Robert Jordan (played in the movie by Gary Cooper - selected by Hemingway himself) is inspired by Hemingway's own experiences as a journalist in Spain. He first went over there in 1931, just after the monarchy of Alfonso XIII had been overthrown. He correctly predicted the civil unrest in the country, and when the Civil War began in 1936, Hemingway wrote articles, delivered speeches, and raised money for the Loyalist cause. In 1937, Hemingway again traveled to Spain to cover the war for the North American Newspaper Alliance. Only a few months after his arrival, Hemingway announced that he was working on a new novel about the war.

He goes alone at first, accompanied only with his Spanish peasant guide Anselmo. Soon they meet a small band of mountain-dwelling Spanish freedom fighters, including the drunken leader Pablo (Akim Tamiroff), his wife, the wise Pilar (brilliantly played by Katina Paxinou), and lovely 19-year old Maria (Ingrid Bergman). Roberto seeks thier support to destroy the bridge, but divided loyalties among the fighters complicate matters. But it is Pilar (which means "pillar" in Spanish) who believes in the mission of Roberto, and convinces the group to proceed and assist with his mission.
One of the guerillas asks Roberta, "Why have you come so far to fight for our republic?" "A man fights for what he believes in", says Roberto, who goes on to explain how the Nazis and fascists were against democracy just as much as they were against the communists.
Directed by Sam Wood, For Whom The Bell Tolls was a HUGE box-office hit in America, well-received by critics and the Academy, who honored the movie with 9 Academy Award nominations. Not only did it have the star power of Coop, but the film, released in the middle of World War II, was also seen as inspirational with its anti-fascist sentiments.

One more thing I want to comment on. After about 90 minutes, there is an intermission. Now I just love how long films back in the day used to have intermissions. Why don't modern movies have intermissions? I mean, really. Who can sit for over two or three hours in a theater seat anyway? Any good chiropractor will tell you that you should never sit that long. So why can't movies like Titanic and King Kong have intermissions? I don't understand this. Sigh!
