Grand Illusion

During the First World War, two French aviators, aristocratic Captain de Boeldieu (played by Pierre Fresnay) and working-class Lieutenant Maréchal (Jean Gabin), embark on a flight to examine the site of a blurred spot on photos from an earlier air reconnaissance mission. They are shot down by a German aviator and aristocrat, Rittmeister (Cavalry Captain) von Rauffenstein (Erich von Stroheim). Von Rauffenstein, upon returning to base, sends a subordinate to find out if the aviators are officers and, if so, to invite them to lunch. During the meal, von Rauffenstein and de Boeldieu discover they have mutual acquaintancesa depiction of the familiarity, if not solidarity, within the upper classes that crosses national boundaries.De Boeldieu and Maréchal are then taken to a prisoner-of-war camp, where they meet a colorful group of fellow French prisoners and stage a vaudeville-type performance just after the Germans have taken Fort Douaumont in the epic battle of Verdun. During the performance, word arrives that the French have recaptured the fort. Maréchal interrupts the show, and the French prisoners spontaneously burst into "La Marseillaise". As a result of the disruption, Maréchal is placed in solitary confinement, where he suffers badly from lack of human contact and hunger; ironically, the fort changes hands once more while he is imprisoned. De Boeldieu and Maréchal also help their fellow prisoners finish digging an escape tunnel. However, just before it is completed, everyone is transferred to other camps. Because of the language barrier, Maréchal is unable to pass word of the tunnel to an incoming British prisoner.De Boeldieu and Maréchal are moved from camp to camp, finally arriving in Wintersborn, a mountain fortress prison commanded by Von Rauffenstein, who has been so badly injured in battle that he has been promoted, but reassigned, much to his regret. Von Rauffenstein tells them that Wintersborn is escape-proof.At Wintersborn, the pair are reunited with a fellow prisoner, Rosenthal (Marcel Dalio), from the original camp. Rosenthal is a wealthy French Jew, a naturalized French citizen, son of a Polish father and Danish mother, who generously shares the food parcels he receives. De Boeldieu comes up with an idea, after carefully observing how the German guards respond to an emergency. De Boeldieu volunteers to distract the guards for the few minutes needed for Maréchal and Rosenthal to escape. After a commotion staged by the prisoners, the guards are ordered to assemble them in the fortress courtyard. During the roll call, it is discovered that de Boeldieu is missing. He makes his presence known high up in the fortress, drawing the German guards away in pursuit. Maréchal and Rosenthal take the opportunity to lower themselves from a window by a homemade rope and flee.Von Rauffenstein has the guards stop shooting at de Boeldieu and pleads with his fellow aristocrat to give himself up. De Boeldieu refuses, and von Rauffenstein reluctantly shoots him in the stomach (though he was aiming for the legs). Nursed in his final moments by a remorseful von Rauffenstein, de Boeldieu laments that their usefulness to society (as aristocrats) will end with this war and that unlike the working class or the middle class, for the nobility, dying in war is a honorable way out. He also pities von Rauffenstein, who will have to find a new purpose in the emerging social order.Maréchal and Rosenthal journey across the German countryside, trying to get to nearby Switzerland. Rosenthal injures his foot, slowing Maréchal down. They quarrel and part, but then Maréchal returns to help his comrade. They take refuge in the modest farmhouse of a German woman, Elsa (Dita Parlo), who has lost her husband at Verdun, along with three brothers, at battles which, with quiet irony, she describes as "our greatest victories." She generously takes them in, and doesn't betray them to a passing German army patrol. Maréchal begins to fall in love with her, and she with him, but he and Rosenthal eventually leave from a sense of duty to the war effort after Rosenthal recovers from his injury. Maréchal declares his intention to come back for Elsa and her daughter, Lotte, after the war.A German patrol sights the two fugitives crossing a snow-covered valley. The soldiers fire a few rounds, but then an officer orders them to cease fire, saying the pair have crossed into Switzerland. We last glimpse the pair from a distance, trudging through deep snow, their future uncertain.

Question: During which war does this movie take place?
Answer: WWI