One of the many great aspects of Casablanca is the role played by the music outside Max Steiner’s background score—almost to the point of being another character in the movie.
The first time Sam plays “As Time Goes By”, the song draws a deep emotional response from Rick who—up to that point—has been cool and indifferent.
And the scene with the dueling songs of the Germans’ “Die Wacht am Rhein” and the French anthem “La Marseillaise” presents a pivotal point in the movie. The moment becomes even more powerful when one considers the backstories of some of the actors who played that scene.
Steiner’s score, of course, shines throughout the movie, but especially during the flashback scenes with Rick, Ilsa and Sam in Paris.
The score starts with the bright broad strokes of strings with harps and a piano, but abruptly darkens as the Germans’ capture of Paris becomes imminent. Steiner uses brass with tight clashing chords as a background to scenes of German bombers, tanks and troops. The brass with smooth drawn-out minor chords supports Rick’s feeling of nervous agitation on the rainy train platform as Ilsa fails to show. He brings back the predominant strings as Rick reads Ilsa’s letter. And then he features the brass again, but softer this time, as the train pulls out with Rick and Sam but without Ilsa.
As an aside, Casablanca also features the musical introduction composed by Steiner for Warner Brothers movies. According to the Steiner biography by Steven C. Smith, Steiner’s intro included no ending so that it could seamlessly segue into the musical theme of the movie it preceded. Casablanca illustrates how well that worked.