How does buck become the leader of the Wolf pack

Buck was challenged by the leader of the pack and responded by breaking his neck. Three others challenged him afterward. He fought and dominated in each fight. In this way, he became the pack's leader.

They were awed, so still and large he stood, and a moment’s pause fell, till the boldest one leaped straight for him. Like a flash Buck struck, breaking the neck. Then he stood, without movement, as before, the stricken wolf rolling in agony behind him. Three others tried it in sharp succession; and one after the other they drew back, streaming blood from slashed throats or shoulders.