Sacrifice
One of the main themes of the film is sacrifice. We watch as Curtis sacrifices his arm in order to save a child from the engine at the end of the film. Curtis' sacrifice echoes the fact that Gilliam sacrificed his arm for Curtis to eat as a younger man, in order to stop him from eating an infant Edgar. Throughout the film, Curtis has shame and guilt about the fact that he has not sacrificed as much as his fellow tail passengers, and in the end, he is finally able to sacrifice himself for the greater good. Additionally, we see the sacrifice of so many people throughout the course of the revolt. In the course of the revolution, many lives are sacrificed for the good of the cause.
Class
Class is a major theme of this film. The separation of classes into different train cars physically represents the strict hierarchy of the train. The tail of the train contains the poorer classes, who are oppressed and beaten down and are only kept alive in order to produce the children Wilford needs to operate the train. As Curtis and the revolt move through the cars, we see the conditions in the cars improved, and it becomes clear that the poor tail passengers are only alive to hold up and sustain the upper classes in the front cars. The film follows Curtis and the others as they stage a revolution against the upper classes. Throughout the film, Wilford and his minions insist that passengers' positions are "preordained" and that it is not within an individual's power to change this stratification. This intense belief in class stratification keeps the tail passengers wanting, and the passengers at the front of the train fat and happy. When Wilford tells Curtis that everyone is meant to stay in their place, Curtis fires back, "That's what people in the best place say to the people in the worst place." This class antagonism is at the center of the film.
Collusion
Collusion is a major theme of the film that we see played out in secret. It is not until the end of the film that we learn that Wilford and Gilliam have been in concert with one another, allies the entire time. The reason for their collaboration is so that they can maintain the population of the train in order to maintain a proper allocation of resources. Curtis is shocked to learn that his mentor and friend Gilliam has been in alliance with the enemy the entire time. Upon learning of this collusion, Curtis rejects Wilford's offer of power and puts an end to the system completely by allowing Namgoong to set of an explosion to destroy the train. Thus, Curtis rejects an opportunity to collude with the evil Wilford.
Guilt
Throughout the film, Curtis feels a tremendous amount of guilt. Primarily, his guilt stems from the fact that he has failed to make an adequate number of sacrifices in order to contribute to the revolution. While others have lost limbs and given up more than him, Curtis feels ashamed of how his body remains intact. Additionally, he feels shame about the fact that he almost ate his friend Edgar when Edgar was an infant. He cries as he tells Nam about the moment he almost ate Edgar, but was saved from doing so by the self-sacrificing Gilliam. Throughout the film, Curtis must contend with his guilt.
Violence
Violence abounds in the film. As the tail passengers rise up, they engage in hand-to-hand combat and brutal battles in order to keep moving through the various cars. Because bullets are scarce in this post-apocalyptic world, the characters must fight with axes, knives, and spears, which makes for highly charged and Medieval instances of violence. We see characters get stabbed, impaled, chopped up, and worse, throughout. When Curtis arrives at Wilford's car, we see that Wilford, as the leader of the train, is protected from this violence by his power, and he has an almost condescending attitude towards violence, even though the violence of the train is precisely what keeps him in power. He calls the violence "pathetic" and "awful," yet also maintains that violence ensures that the train does not become overpopulated.
Nature
Snowpiercer takes place in a post-apocalyptic world in which the earth has been overtaken by an Ice Age, due to human technological interference with global warming. The inhabitants of the train must simulate natural processes on the train. Thus, there is a greenhouse and an aquarium onboard. Outside, however, is a frozen world devoid of greenery. In order to maintain balance on the train, Wilford rationalizes that his fascistic methods of governance are aligned with natural processes, and that his overbearing leadership style is in the service of the "ecosystem" of the train.
At the end, the revolutionaries destroy the train and throw its "natural" balance completely off course, in hope that they might have better luck in the wilderness. Yona and Timmy wander out into the snow, wrapped in furry coats, where they encounter a polar bear, a symbol of the fact that the Ice Age is beginning to thaw, and life on earth is once again possible.
Leadership
In the beginning of the film, Gilliam tells Curtis that he is born to be a leader, but Curtis does not believe him. Curtis wants Gilliam to lead the revolution, but Gilliam insists that he is too old and cannot do so, so Curtis must reluctantly take his position at the head of the group. When he arrives at Wilford's car, Wilford compliments Curtis' leadership, and also reveals that he and Gilliam have been in cahoots the whole time. Wilford has every reason to execute Curtis, but instead he decides to offer Curtis his position at the head of the train, implying that it is exactly what Curtis has wanted all along. In this moment, Curtis' worst enemy, Wilford, offers him a position of leadership. Thinking of the greater good, Curtis declines and attacks Wilford, hoping that by destroying the train itself, he will destroy the oppressive social system in place. The film follows Curtis' ambivalent relationship to leadership, and shows that ultimately, his refusal to become a figurehead on the train is what saves the society from violence and corruption.
