Casablanca is a tale of two songs. The first song, "La Marseillaise," is the French national anthem, written during the era of the French Revolution about fighting for freedom from political repression. In Casablanca, it represents a free France, and, by extension, the Allied side in World War II. The song plays many times throughout Casablanca, most significantly when almost all the patrons at Rick's join in a stirring rendition intended to overwhelm the sound of the Nazi anthem that a few German soldiers are singing. In this dramatic scene, World War II shifts from geopolitical contest to ideological and cultural battle. The war is not only between the Allies and the Axis, but also between the ideals of the French Revolution, liberté, egalité, fraternité (liberty, equality, brotherhood), and the rights of man, and the darker obsessions of the Nazis, including evil, tyranny, and death. In this scene, the patrons of Rick's show themselves to be fiercely pro-Allies. Even the cynically promiscuous Yvonne, who just that evening has shown up with a new German beau, sings with passion and conviction.
"La Marseillaise"may win an easy battle with the Nazi anthem, but it has a harder time defeating the other song that is central to Casablanca, "As Time Goes By." In World War II, the conflict is between the Axis and Allies, while in Casablanca, the struggle is between the public and private. Whenever "La Marseillaise" plays, including as a voiceover describing the plight of political refugees during World War II in the movie's opening and when Louis and Rick walk down the empty runway together with their friendship linked by a new political bond, Casablanca is a film about politics and war. When "As Time Goes By" plays, the film becomes the love story of Ilsa and Rick. Unlike "La Marseillaise," whose meaning never changes, "As Time Goes By" has many roles in the film, each with a different slant. In Paris, "As Time Goes By" was Rick and Ilsa's song, a symbol of their love. In Casablanca, it is a forbidden song that Rick fears will remind him of Ilsa, but which by its absence has come to represent her. When Ilsa does arrive in Casablanca, the song takes on a third meaning. Sam plays the song at both Ilsa's and Rick's request, and it suggests both halves of their relationship: the Parisian idyll and the train station betrayal, as well as the possibility of the love story beginning anew in Casablanca.
"La Marseillaise" isn't played in Rick's Café until after Sam plays "As Time Goes By," and this ordering is significant because we can see that Rick's political apathy relates to his disenchantment with all forms of commitment, both political and personal. Only after Ilsa reawakens his heart by coming to the bar can Rick become politically engaged again. At the same time, the fact that Casablanca begins and ends with "La Marseillaise" suggests that the political is the foundation upon which all things personal happen, including Rick and Ilsa's love story. The actual words of "As Time Goes By" argue that the one timeless truth is love, but in Casablanca, the political ultimately triumphs. Ilsa's return to Rick's life lasts only a few days. When she leaves Casablanca, she leaves Rick forever, but the war is still far from over for them both.