Understanding an Event Associated with Manifest Destiny

During the period of Manifest Destiny in the 19th century, the ideology that the United States was destined to expand across the North American continent significantly influenced American foreign policy and territorial acquisitions. This belief was not only centered on the desire for land but also reflected attitudes toward race, culture, and the perceived mission of the United States. To understand the impacts of Manifest Destiny, consider the events that unfolded regarding territories in the West. Which of the following events or developments is most directly associated with the belief in Manifest Destiny?