Complex sentence: After 49 years at the fort, the U.S. Army left the site in 1912, and the Idaho National Guard occupied it until 1919, when the Public Health Service obtained it for veterans of World War I and tuberculosis patients.
Split into simpler sentences: After 49 years at the fort, the U.S. Army left the site in 1912. The Idaho National Guard occupied it until 1919, when the Public Health Service obtained it for veterans of World War I and tuberculosis patients.