We see multiple forms of violence in this text: dogs attacking each other, men beating dogs, dogs fighting men, and the hunt and kill relationship of predator and prey. It is interesting to compare these forms of violence: which are natural? Which count as abuse? If men use weapons (like clubs or whips) on the dogs, is this an unfair form of violence compared to, say, Buck hunting down and killing a creature weaker than he? These are the types of questions raised in the text.
London's extensive use of violence in The Call of the Wild serves to emphasize the sheer brutality of the wilderness, particularly in contrast to Buck's initial domesticity.
While many changes contribute to Buck's adaptation, he is not a true part of the wild until he adapts to the violence of the natural world.