Final answer:
Americans aimed to expand westward towards the Western Frontier, particularly focusing on the territory that would later be involved in the Mexican-American War.
Step-by-step explanation:
To expand their nation, Americans looked westward towards the Western Frontier, and the nation of Mexico. Specifically, they eyed the annexation of Texas and the lands that would be fought over during the Mexican-American War.
The concept of Manifest Destiny played a crucial role in this movement, suggesting a divine sanction for the expansion and Americanisation of the continent. Significant milestones of this expansion include the Louisiana Purchase from France, the expeditions of explorers like Lewis and Clark, and the forced movement of Native American populations onto reservations.