Complex sentence: He made four expeditions, two to the plains tribes of Kansas and Nebraska, and two more up the Missouri River past Yellowstone, before the development of any inland transportation system, when Bison and other game could be shot for food from riverboats on the Missouri.
Split into simpler sentences: He made four expeditions, two to the Plains tribes of Kansas and Nebraska, and two more up the Missouri River past Yellowstone. This was before the development of any inland transportation system, and passengers could shoot Bison and other game for food from riverboats on the Missouri.