Why does Buck want to be the leader in the Call of the Wild?

Buck doesn't simply want to be the pack's leader, he wants to have complete dominance. Buck's biggest challenge is Spitz, and the other dog is a formidable rival. Eventually, as Buck and the other dogs are starving and struggling to survive, a rabbit is spotted. Buck and Spitz fight to the death over the rabbit, something which is realy far, far more than the hunt. Buck prevails and takes over as leader.