Final answer:
Manifest Destiny influenced many Americans to participate in westward expansion, justified by beliefs of their destiny to spread democracy across the continent and the Americanization of existing populations.
Step-by-step explanation:
In the 1800s, many people in the United States acted on the idea of Manifest Destiny by engaging in westward expansion movements to fulfill what they believed to be their destiny to spread democratic institutions across North America. This concept justified not just territorial expansion but also the Americanization of indigenous populations and Mexican residents in territories like Texas, Oregon, and California.
The pursuit of Manifest Destiny led individuals to expand the nation's boundaries, expecting that their expansion would spread freedom and democracy "from sea to shining sea." It was also fueled by economic motivations as private individuals engaged in commercial and agrarian endeavors in frontier areas.