Answer: Expansion from the Atlantic to the Pacific
Step-by-step explanation:
The United States was originally 13 states on the Atlantic coast but today covers a vast area from the Atlantic to the Pacific. This is as a result of the Manifest Destiny mindset that engulfed America in the 18th and 19th century.
Those who subscribed to the Manifest Destiny believed that it was the destiny of the United States to stretch from the Eastern coast where the Atlantic was, to the Western Coast where the Pacific was.
As a result, Settlers went to the Western regions by their thousands and displaced natives, often violently, and took over their land as well as went to war with Mexico for the country to look as it does today.