The internal conflict is that which exists within Buck between the civilized and the wild worlds. At the beginning of the story, he's a normal, domesticated dog living in comfort in the San Francisco area. When kidnapped and forced to serve on a sled team in the "Northland," a huge transformation occurs in his life. At the end of the story, this process of change is complete when Buck has joined a wolf pack as its leader. He's gone from one extreme to the other—complete comfort and domesticity to the condition of his remote ancestors in the wild.
Externally Buck is in conflict with his captors and with other animals in the sled team. The cruelty of both humans and animals, even prior to his transition into the fully uncivilized world (though this is a human-directed negation of the civilized), is what Buck has to contend with in order to stay alive. But arguably the conflict both external and internal occurs as a result of Buck's rescue and adoption by John Thornton.
His time with...
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