Complex sentence: Fort Chadbourne was a fort established by the United States Army on October 28,1852, in what is now Coke County, Texas, to protect the western frontier and the Butterfield Overland Mail route.
Split into simpler sentences: Fort Chadbourne was a frontier fort established by the United States Army in what is now Coke County, Texas. It was established October 28,1852, to protect the western frontier and the Butterfield Overland Mail route.