"Louis, I think this is the beginning of a beautiful friendship." Humphrey Bogart's famous exit line has always been one of my favorites, but I have never really thought about the line in context to the rest of the movie. To me, this line is very indicative of how Rick changes throughout the film, and how his personal changes affect the people around him. At the beginning of Casablanca, Rick Blaine doesn't seem to be the type of guy who has a whole lot of beautiful friendships, does he? He is the supreme cynical observer, never drinking or interacting with his customers, a grab-bag of nationalities stuck in the purgatory of Casablanca and Nazi and Vichy French officers. Though Rick claims to be completely neutral, he has in the past fought against the Nationalists in the Spanish Civil War and allows illegal exit visas to be sold in his nightclub. This neutral, cynical shell begins to crack, however, from the moment Ilsa Lund walks into Rick's club and back into his life.
Upon Ilsa's arrival, we learn that she and Rick were lovers in Paris up until the German occupation. We also learn that Rick is not nearly as cynical or disattached as he wants his Casablanca cohorts to believe. A few days after Ilsa and Victor's arrival, Rick seriously breeches his modus operandi by helping a young couple obtain the money for exit visas so the woman could escape to America and still remain loyal to her husband. It is at this moment that we realize loyalty means something to Rick, no matter the opportunist personal philosophy he expounds. As the story progresses and Ilsa finally gives Rick the reason she never met him to escape Paris, Rick once again respects her loyalty to her husband, Victor. Though no one in the film overtly mentions loyalty as an important theme, it seems to surround Rick. His friends and employees are endlessly loyal to him, Ugarte trusts Rick to by loyal to the Underground cause by entrusting him with the letters of transit, and in the end even the morally unscrupulous Renault expresses loyalty towards Rick by choosing not to narc on him when he shoots a German officer. Rick himself is in the end loyal to the cause of fighting the Nazis, expressing this sentiment in his sacrifice of his relationship with Ilsa so Victor's work can continue.
Something I have never really noticed in watching Casablanca that I picked up on this time is the parallel between the film characters and the countries participating in World War II. Rick and his pianist Sam are the only Americans in the film, and are representations of the United States itself. Rick seems to embody the neutral, isolationist side of America, while Sam and his music represent the hope offered by America to all of the people who come to Rick's club in hopes of eventually reaching the United States. Rick's actions also reflect the actions of the U.S. during the course of the war. At the beginning of the film, Rick takes care of his customers but does not get directly involved with them, much like the U.S. took measures to help the Allied side while maintaining neutrality in the beginning of the war. At the end of the film, Rick's involvement saves the day, just like the American troops' entrance into Europe changed the tide drastically (at least according to the American point of view).