Sentence:  Activity by British traders and the presence of a colony on the <WSD>Red</WSD> prompted the United State War 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 tributary of the Mississippi River that flows eastward from Texas along the southern boundary of Oklahoma and through Louisiana