How was the manifest dynasty used by U. S. leaders as a way to explain their continental expansion?

James K. Polk, considered the last strong president before the civil war, was very immersed in the theory of manifest destiny and he commanded the USA in the war agaisnt Mexico and the subsequent gaining of vast territories for America.

Explanation: The manifest dynasty was used by the American leaders as if it were a doctrine based on the prediction that consisted in that this country had as a natural purpose to expand into territories other than its own and to be able to use the resources that these conquered territories possessed to concretize Its expansionist moods. For these purposes, the American leaders used their strength to provide protection to those underdeveloped nations and fight against the evils that afflicted those nations, arguing that they were able to defend the freedom of these repressed peoples, but this was no more than a pretext to achieve its objectives of expanding into new territories.