Fort Union and Fort William offers a window into the fur and bison robe trade of the early 1830s, building upon the previous work of editors W. Raymond Wood and Michael M. Casler in Fort Tecumseh and Fort Pierre Chouteau: Journal and Letter Books, 1830-1850, published by the South Dakota Historical Society Press in 2017. The documents Wood and Casler have compiled and annotated include newly transcribed letters from Robert Campbell and William Sublette, providing two sides of the extraordinary story of the fur trade on the Northern Great Plains.