Answer:
In the nineteenth century, the doctrine of Manifest Destiny was a common belief among the inhabitants of the United States that American colonizers should expand in North America, from the Atlantic to the Pacific. It expressed the belief that the American people were elected by God to civilize their continent.
The Manifest Destiny was not a thesis embraced by all American society. The differences within the country itself about the objective and consequences of the policy of expansion determined its acceptance or resistance.
The northeastern states believed for the most part that the United States should take its concept of "civilization" throughout the continent through territorial expansion. In addition, for US commercial interests, the expansion offered large and lucrative access to foreign markets and thus allowed to compete in better conditions with the British. Having ports in the Pacific would facilitate trade with Asia.
The southern states sought to extend slavery. New slave states would strengthen the power of the south in Washington and would also serve to place the growing slave population.
This north-south conflict became clear with the question of Texas's entry into the Union and was one of the main causes of the future Civil War.
There were also political groups that saw the excessive territorial extension as dangerous; they believed that their political system and the formation of a nation would be difficult to apply in such a vast territory. This position was defended as much by some leaders of the Whigs as by some expansionist Republican-Democrats, who argued about how much territory should be acquired.
Another point of discussion was the use of force. Some political leaders (whose maximum exponent was James K. Polk) did not hesitate to try to annex the largest possible territory even at the risk of triggering wars (as in fact happened) with other nations. Others opposed (albeit timidly) the use of force, on the grounds that the benefits of their system alone would suffice for the territories to join voluntarily.
It can be said that the own supporters of the "Manifest Destiny" formed a heterogeneous group with different interests.