Final answer:
The Burlington & Missouri River Railroad Co. sold land due to financial difficulties, government incentives, and excess land holdings.
Step-by-step explanation:
The historical circumstances that led to the Burlington & Missouri River Railroad Co. selling millions of acres of land in Iowa and Nebraska were multifaceted. First, the company faced financial difficulties and needed to generate revenue to sustain its operations. Second, the U.S. government provided incentives for railroad companies to sell land to settlers as a means of promoting westward expansion and development. Lastly, the company's land holdings exceeded its operational needs, and selling the excess land was a way to monetize those assets and encourage settlement in the regions.