Most explorers accessed the Great Plains and Southwest during the early 1800s by way of the __________ River
To find the answer to this question, we can consider the historical context and the major rivers in the regions mentioned.
During the early 1800s, explorers were often searching for new lands, resources, and trade routes in North America. The Great Plains and Southwest regions of the United States were less explored at that time.
One of the major rivers in this area is the Missouri River. It stretches across the Great Plains, running through states like North Dakota, South Dakota, Nebraska, and Missouri. The Missouri River is the longest river in North America and was a significant route for exploration and westward expansion during the early 19th century.
Therefore, the answer to your question is that most explorers accessed the Great Plains and Southwest during the early 1800s by way of the Missouri River.