Complex sentence: Detachments from Camp Cooke guarded major transportation routes in Southwestern Montana, including the roads between Fort Benton and Helena, building Fort Shaw along that route in 1867 in the Sun River Valley.
Split into simpler sentences: Detachments from Camp Cooke guarded major transportation routes in Southwestern Montana, including the roads between Fort Benton and Helena. They built Fort Shaw along that route in 1867 in the Sun River Valley.