If it was truly America's destiny to reach the Pacific ocean, to expand westward as far as possible and conquer all resisting peoples, that destiny was accomplished. However we raise the question once again, at what cost was this expansion made possible? Thousands of lives lost, Mexicans, Americans, and Native Americans. A war was brought on and resources were spent all to reach that golden California coast. Lives were once lost for the Independence of America, was freedom from Britain a more just cause of bloodshed than westward expansion? I believe the answer is that destiny or not, the United States had an agenda, they had the resources and the man power to accomplish their goals. They justified accomplishing these goals by proclaiming that it was their God ordained manifest destiny and if that meant war, than so be it. From a Mexican point of view we might see this as a failure, a failure for their "destiny." Mexicans believed they had a right to their territory, and a lot of citizens and soldiers believed it should be fought for. Some government officials believed they had a duty to their people over their land. Unfortunately opposing ideas would lead to the failure to maintain all of their territory. Perhaps they believed it was a small price to pay over being annihilated by the American forces. Some Mexicans would realize they did not stand a chance against the Americans and perhaps if it was American destiny, this would hold true. I believe there is no justification for war, no destiny should be obtained through bloodshed.
"Although most Americans believed in manifest destiny, few could agree on exactly which lands the United States was supposed to govern." -Charles W. Carey Jr.
Occupation of Mexico City by American Forces in 1847 https://en.wikipedia.org/wiki/Manifest_destiny