When we look at the era of Manifest Destiny through our present-day values, it is clear that we did not fulfill this destiny in a just way. In fact, it is hard to even conceive of how we might have done so. The entire idea of Manifest Destiny is hard to reconcile with our current ideas about justice.
The idea of Manifest Destiny held that we essentially had the right to take territory from other peoples because we were superior to them in various ways. There is simply no way to see this as a just ideology today. It would be one thing if the various people whom we conquered asked to be annexed into the United States. The problem was that they did not. Given our current values, taking land from others cannot be just.
What is more, we were willing to commit greater and lesser acts of violence to get that land. Perhaps the least violent thing we did was to coerce the Hawaiian monarchy to give up its sovereignty at gunpoint. But we also killed large numbers of Native Americans, fought a war against Mexico, and fought a very bloody war against Filipinos. All of these things were done as a way to take the land we believed we were destined to have.
Thus, our ends cannot now be seen as just and neither can our means. At the time, the things we did to fulfill our “Manifest Destiny” were essentially justifiable by contemporary moral standards. Today, they are not.