Final answer:
The central idea of the 'Moving West' section is the concept and necessity of westward expansion in the mid-nineteenth century.
Step-by-step explanation:
The central idea of the 'Moving West' section is the concept and necessity of westward expansion in the mid-nineteenth century. This idea was idealized in Manifest Destiny, which emphasized the responsibility to conquer, inhabit, and prosper in the new lands.
The section highlights the various groups involved in the westward movement, such as settlers, cowboys, miners, soldiers, and explorers, as well as the factors that contributed to westward migration, such as the discovery of gold in California and the construction of railroads.