The Plains Indians were almost totally dependent upon the bison. They were a source of food, shelter, utensils, and clothing and most importantly spiritual strength. The American bison sacrificed its life to keep the American Indian in existence.
The Kansas River stop was most likely the most dangerous stop of the Oregon Trail.
Rivers crossing was usually dangerous for settlers with unpredictable tides ran the risk of drowning, losing livestock, losing important supplies, or overturning wagons.
It's not the middle or the west of the US. Because when the US was expanding in the 19th century - and when many regions were initially being named - the “Midwest” was to the west of the main population centers in the “13 colony” states on the Eastern Seaboard
