Final answer:
The U.S. government promoted western migration during the Civil War to discourage the expansion of slavery and increase agricultural output. They also aimed to connect the country through the construction of the transcontinental railroad.
Step-by-step explanation:
The U.S. government promoted western migration during the Civil War for several reasons. First, they wanted to discourage the expansion of slavery in the newly settled territories. By encouraging free-labor farmers to move west through the Homestead Act, the government hoped to populate the region with allies who opposed slavery. Additionally, the government aimed to increase agricultural output for the war effort by incentivizing farming in the West. They also recognized the strategic importance of connecting the country by rail, leading to the construction of the transcontinental railroad.