When, in 1883, Congress charged the US Army with managing Yellowstone National Park, soldiers encountered a new sort of hostility: work they were untrained for, in a daunting physical and social environment where they weren't particularly welcome. When they departed in 1918, America had a new sort of serviceman: the National Park Service Ranger. From the creation of Yellowstone National Park to the conclusion of the army's superintendence, Watching...