Final answer:
Mountain men, by participating in the westward expansion, contributed to the early stages of Manifest Destiny, but their individual beliefs on the doctrine would have varied. Manifest Destiny provided a divine justification for American expansion, cultural assimilation of other populations, and the spread of American values and polity during the 19th century.
Step-by-step explanation:
Mountain men were part of the early westward expansion movement that preceded the widespread adoption of the ideology of Manifest Destiny in the 1840s. While not all individuals may have explicitly professed belief in Manifest Destiny, the actions of mountain men—exploring, trapping, and trading in the West—certainly contributed to the nation's expansionist tendencies. It's important to note, however, that individuals' beliefs varied, and not all mountain men may have seen their actions through the ideological lens of Manifest Destiny, which was rooted in the belief of a divinely ordained mission to spread American values and political systems across the continent.
Manifest Destiny was a powerful motivator for many, as it justified American expansion and the inevitable cultural and political influence over other populations already inhabiting North America, such as Native Americans and Mexicans. As the United States pushed its frontiers westward, figures like Senator Thomas Hart Benton vocalized this sentiment, asserting that Americans were chosen by God to control the Western Hemisphere, from sea to shining sea. This expansion was further characterized by significant demographic shifts, economic opportunities like the California Gold Rush, and major infrastructure projects like the railroad system, all of which were parts of fulfilling the country's perceived Manifest Destiny.