Final answer:
The main objective of Manifest Destiny was the westward expansion of American territory, aiming to spread the United States across the continent, which included the Americanization of native populations and viewed expansion as a spread of freedom.
Step-by-step explanation:
The main objective of those who believed in "Manifest Destiny" was the westward expansion of American territory. This concept included the belief that the United States was destined to expand across the North American continent, from the Atlantic to the Pacific Ocean, a notion often summarized as "from sea to shining sea." The ideology also involved the Americanization of indigenous peoples and other residents of the territories, as well as the idea that expanding the boundaries of the United States was synonymous with spreading freedom and democracy. Essentially, Manifest Destiny provided a moral and cultural justification for American territorial expansion during the 19th century.