What event causes Buck to truly answer the call of the wild?

The death of John Thornton is a pivotal moment in "The Call of the Wild" that profoundly impacts Buck and propels him toward embracing his primal instincts and the call of the wild. John Thornton represents the last connection Buck has to humanity and a life of comfort and companionship. Thornton's unwavering kindness and dedication to Buck establish a deep bond, showcasing the loyalty and love that Buck is capable of feeling.

When Thornton is killed, it shatters Buck's remaining ties to civilization and safety, forcing him to confront the brutal reality of the wild. This loss catalyzes Buck's transformation as he begins to heed the instincts that have been building within him throughout the story. The death signifies the moment when Buck fully embraces his wild nature, allowing him to answer the call of the wild and ultimately live freely as a creature of the forest, no longer encumbered by his former life.