How did the idea of ManifestDestiny help Americans justify their desire to extend the US to the Pacific Ocean?

Americans believed that G-d's will was that America be extended "from sea to shining sea." This is another version of an empire's belief that G-d is on the side of the emperor and the imperial design.

That is what manifest destiny is. Manifest Identity is the idea that the U.S. Should span from the Atlantic Ocean to the Pacific Ocean. Therefore they justified expanding it

Americans wanted a free land where people could practice their religion freely.

Manifest Destiny was a phrase that expressed the belief that the United States was destined to expand from the Atlantic seaboard to the Pacific Ocean; it has also been used to advocate for or justify other territorial acquisitions. Advocates of Manifest Destiny believed that expansion was not only good, but that it was obvious ("manifest") and certain ("destiny"). It was originally a political catch phrase or slogan used by Democrats in the 1845-1855 period, and rejected by Whigs and Republicans of that era. Manifest Destiny was an explanation or justification for that expansion and westward movement, or, in some interpretations, an ideology or doctrine which helped to promote the process. This article is a history of Manifest Destiny as an idea, and the influence of that idea upon American expansion.

The phrase "Manifest Destiny" was first used primarily by Jackson Democrats after 1845 to promote the annexation of much of what is now the Western United States (the Oregon Territory, the Texas Annexation, and the Mexican Cession). The term was partly revived in the 1890s, this time with Republican supporters, as a theoretical justification for U.S. expansion outside of North America. Opponents such as Abraham Lincoln wanted vertical modernization with greater complexity and specialization, instead of the horizontal expansion of simple farms. As Lincoln explained, he "did not believe in enlarging our field, but in keeping our fences where they are and cultivating our present possession, making it a garden, improving the morals and education of the people."[1] Historian David Potter concludes that in 1854 the Ostend Manifesto and the Kansas-Nebraska Act were "the two great calamities of the Franklin Pierce administration.... Both brought down an avalanche of public criticism." More importantly, says Potter, they permanently discredited Manifest Destiny and popular sovereignty. [2]

The term fell out of usage by U.S. policy makers early in the 20th century, but some commentators believe that aspects of Manifest Destiny, particularly the belief in an American "mission" to promote and defend democracy throughout the world, continued to have an influence on American political ideology.[3]

Manifest Destiny is the belief many settlers first held that said, pretty much, that God had ordained them to control North American from Atlantic to Pacific. Since they felt that God gave them this right, that meant that any obstacles in the way, like the Native Americans, were savages that could just be destroyed with no remorse. In short, justification of any actions in the name of God. (And I don't believe their ways justified their means.)

Europeans have always thought the world was theirs for the taking, guess that karma stuff is starting to catch up now though. Glad to see it myself (the karma thing).