Dana Polan discusses how American cinema changed during WWII as it began to reflect propagandist messages and wartime affirmation. However, creating films that had both propaganda and entertainment value was not an easy task. Filmmakers had to seamlessly tie together a Hollywood story and a larger narrative of war engagement. Casablanca is an example of a film that successfully executed the duality of entertainment and propaganda by using the  "conversion narrative", a narrative in which a person who is indifferent and cynical about the war converts to become involved and supportive of the war effort.
    A supreme example of "conversion narrative" can be found in the character development of Rick. His initial cynicism ultimately gives way to a commitment to a greater good. Despite his final decision, the ending of the film remains ambiguous and viewers are uncertain of what the characters will do when they part, and more importantly how the war will end. In this sense, viewers at the time of the films release could relate to the ambiguity of the characters onscreen, as they too understand the concepts of love, loss, and confusion during wartime. Rick's conversion process makes him a much more identifiable character with American audience compared to the clear-cut and one-sided narrative that surrounds Lazlo. Rick is human in his multi-faceted nature and is therefore a character that speaks to the American audience, making him the perfect mouthpiece for political messages.

Polan, Dana. "Stylistic Regularities (and Peculiarities) of the Hollywood World War II Propoganda Film." WARNERS’ WAR: POLITICS, POP CULTURE & PROPAGANDA IN WARTIME HOLLYWOOD. pp. 38-47

World War II significantly changed American cinema. Not only were new propagandist messages infused into most films, the actual narratives changed to reflect the new wartimes. Propaganda did not come easy to Hollywood films that had built up a tradition of creating apolitical escapist films. Some films were awkward in their addition of political messages. Many used direct addresses to the audience through the use of voice over or radio newscasts. The heart of the change, however, was in the way romance was treated.

With the clear separation of men and women during wartime, there was an increased feeling that romantic relationships were frivolous and hurt the war movement. This led to a change in the dynamic of on screen couples. Many films were made about woman going to join the men on the battlefront, or the opposite: having the men come home to the woman in America.

One way to view Casablanca is as a romance movie built on separation. The separation of Ilsa from Lazlo in Paris and the night that she asks Rick for the letters of transit, and the separation of Rick and Ilsa when she leaves on the train in Paris. The ambiguous ending of the film in which we are uncertain of what the characters will do when they part, and how the war will end. This reflects the feelings of many Americans throughout the time. The complicatedness of Rick’s feelings towards the war and Ilsa make his character much more identifiable with most Americans compared to the straight forward Lazlo. The movie is a reflection of the time.