Answer:
"Casablanca" was born more as a political propaganda film than as an immortal love story, whose exoticism would be reconstructed entirely in the studios. The Paris station, for example, was recycled from another Warner film, "The Strange Passenger".
The "Casablanca" script was written during a manifest, World War II had left Hollywood without heartthrobs and Humphrey Bogart had joined the cast of the last-minute film, replacing none other than Ronald Reagan. Instead of Ingrid Bergman, the producers had been thinking about Hedy Lamarr, while the film would not even be set in Morocco, but in Lisbon.
At first, the film would have the same title as the theater work on which it was based, "Everybody comes to Rick's", but this idea was eventually discarded in an attempt to repeat the same success of "Algeria", shot three years earlier.
Thus, stumbling, one of the films with the most unforgettable and remembered moments in cinema was developed. The fact is that, with three Oscar awards won, a plot full of unforgettable dialogues, anthological interpretations by Bogart and Ingrid Bergman (as well as Claude Rains and Peter Lorre in secondary roles) and a song by Max Steiner, "Casablanca" would go on forever to Eternity.
Rick and Ilsa, the lovers that time and history will continually want to separate, gave the classic Hollywood melodrama an added bit of bitterness, topped off with that realistic ending so unaccustomed at the time. An inopportune love, whose power will no longer be able to overcome adversity, but mere convenience. That was a hard blow for the second chance and a victory for the defeat.
Given that Paul Henreid and Claude Rains only arrived on the film sets later due to overwork in the previous film, the first scene filmed by Bogart and Ingrid was the meeting at the piano, but the chemistry has since become evident.
They were a perfect couple within the magic of cinema, since he had to climb in boxes to gain the five centimeters that the Swedish actress took from him. Although the song that reminded them of the past is called "As time goes by", this scene ended up being frozen in the retinas of the moviegoers.