Buck uses civil disobedience when he refuses to get up.
Civil disobedience is acting in protest, but in a nonviolent way. Being passive aggressive, and not doing what you are told or not being compliant, is one form of civil disobedience.
When the team of dogs enters John Thornton’s camp, they are exhausted. Buck, who is the leader, collapses. So do all of the other dogs. The men try to get them up, but Buck refuses. Hal yells at Buck, and hits him, but it has no effect.
But the team did not get up at the command. It had long since passed into the stage where blows were required to rouse it. The whip flashed out, here and there, on its merciless errands. (ch 5)
When Buck refuses to stir, he is acting not just for himself but also for the other dogs. They are spent. Hal and Charles have no idea what they are doing, and their foolish actions will kill them all.
It is civil disobedience because Buck does not attack. He just refuses to do what he is asked.
It is Buck’s civil disobedience that saves him. John Thornton watches, at first content to do nothing. Yet when he sees Buck being savagely beaten and unable to get up, he finally intervenes. Unfortunately, he only saves Buck. The others go on and are swallowed up by the collapsed trail.