In Chapter 1, the man in the red sweater captured Buck and then beat him.
In Chapter 2, Buck saw how the dogs acted, with violence. They knew about the law of club and fang, and attacked Curly. She ended up dieing and Buck realized what the club of fang was.
In the beginning of chapter 3, Dolly ended up having a thorn throat. Later on, we learn that she has rabies. She goes crazy with the other dogs, and went for Bck who had never seen a dog act like that. Buck runs away and then the dog-driver used his axe on Dolly's head.
At the end of chapter 3, Buck wants to fight Spitz because Spitz took his bed. All of the dogs are circling around them to watch them fight. In the end, Buck manages to break both of Spitz's right and left fore legs by biting him.
At the very end of chapter 4, Dave became sick. The Scotch half-breed replaced Dave with Sol-leks. Though Dave refused to give up his spot. But Dave ends up dying and then was harnessed.
In chapter 7, John Thornton was found dead. Buck was heading back to the camp when he found out that John was killed by the Yeehat tribe.