Sentence:  Activity by British traders and the presence of a colony on the Red prompted the United State <WSD>War</WSD> Department in 1819 to send Lieutenant-Colonel Henry Leavenworth from Detroit to put a post 300 miles northwest of Prairie du Chien , until then the most advanced United States post . 
Meaning of the word marked with <WSD> tags:  a former executive department of the United States government; created in 1789 and combined with the Navy Department in 1947