Answer:
He is referring to the right of U.S Citizens to fulfill their manifest destiny.
Explanation:
Manifest Destiny was the idea that American civilization, and American people, had the divine, moral, ethical, economic, and political right to spread from the Northeast to the West Coast, and occupy the entirety of the North American Continent.
This idea was justified under a belief of American cultural superiority and exceptionalism over other cultures, for example, Native American Culture. This ideology was materialized during the nineteenth century because by the end of this period the United States had occupy the continental land that stretches from the East Coast to the West Coast, and from the Gulf of Mexico and the border with that country, to the Great Lakes and the border with Canada. In other words, by the end of the XIX century, the modern continental U.S. had already formed.
