The author wrote this a few years succeeding the Klondike Gold Rush and explored its horrors. The Yukon of the early 20th century wasn't as it is today. It was barren, and hard on the body and mind.
Dogs like Buck were cheap, and animal cruelty was common, leading many to criticize London of glorifying and condoning animal abuse.
The atrocities committed against Native tribes in the name of "Manifest Destiny" were thought of as just and honorable in the wake of the Great Indian Wars that wiped out the cultures across the United States. This book is often criticized due to its dark theme, and although it's written from a dogs point of view, really depicts and analyzes the then tense political climate.