Call of the Wild by Jack London.
The story mostly takes place in the Yukon during the Klondike Gold Rush. The main character is Buck, a domestic ranch dog stolen from California and sold off as part of a dog sled team that works the Gold Rush. Having once been a tame ranch dog, he reverts to being wild in order to survive the harsh conditions he endures with several owners. The setting is crucial to every element of the story.
The plot involves various cruel humans that come to own Buck. All of these subplots involve activities that could only take place in the harsh Yukon environment. Taking the story out of that would completely change it.
The dog, the main character, is part of a sled dog team. Without the backdrop of a snowy, cold environment like the Yukon, the character could not be described believably as a sled dog.
The theme involves adventure and survival in the cold snow and extreme landscape of the Yukon. If the setting were different, the theme of adventure and survival would not be as exciting and extreme.