Why is "An Episode of War" considered naturalistic?

"An Episode of War" was written by Stephen Crane. It is a vivid war story. The story is in part about a typical scene that occurred during the Civil War. An officer becomes injured, and he stumbles over to the medical treatment area to get treated. An amputation of the affected limb is needed.
The tale is considered to be naturalistic because the storytelling evinces a belief in nature's indifference about the hopes, aspirations, and needs of the human race. The concept of fate is promoted throughout the story, which means that the humans in the story are limited in their ability to determine their own destiny.
Under this viewpoint, humans are not an integral part in shaping the course of events or their own future. For example, the characters in the story are unnamed, which displays the story's theme of nature's uncaring spirit. The Civil War simply rages on its own, and the soldiers are merely game pieces in the game of life; nature is determining the outcome. The soldier's arm amputation was set in motion by acts of nature, and his desire to keep his arm is irrelevant.
The doctor's behavior in the story is a great example of the naturalistic storytelling. He recognizes that there is no point in trying to resist the fate that nature has ordained. He does not show any caring for the man's arm. He probably could have saved the man's arm. But he lets nature take its course because he believes fighting nature is pointless.