The name of the Indian group that attacked John Thornton is the Yeehats.

In the last chapter of the book, Buck returns to camp only to find that John Thornton and his fellow explorers are dead. Buck first finds Nig (one of John Thornton's dogs) in a thicket. The latter is dead, with arrows protruding from either side of his body.

Next, Buck finds one of the sled dogs in the final throes of death. He passes by the struggling canine and comes upon the dead body of Hans (one of John Thornton's partners). There are many arrows sticking out of Hans' dead body.

By the time he encounters the Yeehats, Buck is furious beyond control. He leaps at them with unsparing rage. First, he rips the throat of the Yeehat chief. Then, he tears at the flesh of every Indian celebrating the deaths of John Thornton, Hans, and Pete. Buck is relentless in his attacks, and he moves so swiftly that none of the Indians can impale him with their spears. In the end, the beleaguered group panics and flees into the forest. The Yeehats contend that they have been visited by an evil spirit. Undeterred, Buck pursues them.

In subsequent days, the tribe is forced to scatter far and wide over the country.

After the Yeehats disperse, Buck returns to camp. He finds Pete, who appears to have been killed in his sleep. At the edge of the pool, Buck finds Skeet, who remained faithful to his master until the last. In the pool itself, Buck finds John Thornton's body. For a time, Buck mourns the death of his beloved friend. With Thornton's death, the "last tie was broken. Man and the claims of man no longer bound him."

The story ends with Buck reclaiming his wolf heritage and becoming the leader of a pack of wild wolves.

The name of the ferocious tribe was the "Yeehats."  The attack occurs in Chapter 7.  Buck comes upon the maurading band:

"The Yeehats were dancing about the wreckage of the spurce-bough lodge when they heard a fearful roaring and saw rushing upon them an animal which they had never seen before.  It was Buck, a live hurricane of fury, hurling himself upon them in a frenzy to destroy....It was a fateful day for the Yeehats.  They scattered far and wide over the country and it was not until a week later that the last of the survivors gathered together in a lower valley and counted their losses.  As for Buck...he found Pete where he had been killed...Thornton's desperate struggle was fresh-written on the earth..."