The main external conflict is man vs. nature. The conflict is shown by the differences between the Southland, symbolizing civilization, and the Northland, symbolizing the savage forces of nature. Buck is ill-prepared for the cold, frozen North compared to the warm, comfortable life he led in the South. He first must survive the beatings by the man in the red sweater, and then survive in his life as a sled dog. Francois, Perrault, and the other dogs teach Buck quickly what he needs to know to survive. Not only does he just survive, he becomes like a wolf. In the end, he's a legendary animal in stories told by the Yeehats, the natives of the Northland.
The main internal conflict is Buck vs. his instincts, which have been suppressed by living in the Southland, and his struggle to be able to answer "the call of the wild" by discovering instincts from long ago. London, the author, anthropomorphizes the dogs, so Buck is treated in the same manner as a human. When Buck faces the man in the red sweater, his pride won't let him give up at first, but he learns the danger of a man with a club. Once he becomes a sled dog, he dreams of the "hairy man" from long ago and unearths the instincts of his wild relatives. The longer Buck lives in the North, the more he becomes a dog of the wild. In the end, he runs free as head of a pack of wolves, having completely answered "the call of the wild".