When the Army Ruled Yellowstone Guest: Thomas Rust, Professor, History, Montana State University, Billings, and author, “Watching Over Yellowstone: The US Army's Experience in America's First National Park, 1886–1918” Creating Yellowstone National Park was quite a feat to begin with, but managing and patrolling it was quite another. For 32 years, the US Army protected  the park and provided a pattern for the Ranger system. They had to deal with poachers practicing guerrilla warfare, hawkers setting up shop, and even boredom and desertion.