In which region was the Fort Union Trading Post located?

The Fort Union Trading Post was located in the Upper Missouri region, specifically on the banks of the Missouri River near the North Dakota-Montana border. This strategic location made it an essential hub for trade between various groups, including Native American tribes and European-American fur traders during the 19th century.

The trading post was established in 1828 and played a significant role in the fur trade, facilitating commerce and cultural exchanges in the area. The Upper Missouri region was vital for this activity due to its access to fur resources and transportation routes along the river. The establishment of Fort Union contributed to the economic development of the region while also illustrating the historical interactions among different cultures during that period.

In contrast, the other options do not accurately reflect the location's historical context. The western and eastern parts of North Dakota are significant, but they do not include Fort Union, and southern North Dakota, while having its own historical relevance, does not pertain to this particular trading post. Understanding the geographical and historical significance of Fort Union in the context of the Upper Missouri region helps illuminate why this answer is the most accurate.