Ok, here goes an attempt:
The history of one culture conquering another, and the other's territory, is nearly as old as humanity itself. Stronger and more devious cultures always have found pastures belonging to weaker cultures to be greener, waters to be sweeter, spices more abundant, gold easier to find, etc. Things do not go well for the conquered. Often they are killed, raped, and/or enslaved. In some instances--and this happened quite frequently in pre-Columbian North America--the conquered culture is merely driven from its land. In still other instances (think of the French conquest of England or the English conquest of Ireland), the conquered are allowed to remain, but subject to the complete rule of the conqueror and forced to assimilate into the conqueror's culture.
The Romans and the British/Americans took a different approach. The Romans did not force assimilation and in fact adopted elements of the cultures they conquered. (That's why Roman mythology looks just like Greek mythology but with the names changed.) They allowed their conquests to retain vast elements of their culture, including self-governance (think of the Israelites), as long as the conquered culture remained submissive. At even the inkling of an uprising, the Romans would act brutally (think of gladiators, slaves, and the destruction of the Second Temple). The British/Americans forced natives to move off of their lands and onto reservations, made and broke series of treaties, but allowed the natives to self-govern. Like the Romans, the British/Americans adopted some elements of some of the native cultures; we celebrate Thanksgiving and had "Indian head" nickels, etc. But this so-called permission to self-govern (affirmed just today by the Supreme Court) again relies upon the conquered culture remaining submissive. When there were uprisings, some of which were manufactured by the British/Americans, the British/Americans acted brutally just as the Romans did. At times, the British/Americans acted brutally even without an uprising, such as the Trail of Tears, and I'm sure the Romans did, too. But the bottom line remains that both of these conqueror cultures set aside land for the peoples they conquered and allowed some degree of independence. To the best of my recollection, those are the only two such instances in history.
Does this mean that the native Americans were treated fairly? Absolutely not. The constant making and breaking of treaties alone demonstrates the opposite. But consistently across human history, on every one of the six populated continents, the conquered culture never is treated fairly. It doesn't matter if it's the Mongols conquering the Rus, one African tribe conquering another, one Native American tribe conquering another, or the Spanish reconquista, the conquered culture loses. It is part of the story of humanity and it is sad.
Would I rather be in the position of a Native American today than in the position of a Scot oppressed by the British or a Congolese under Belgian rule? I can't answer that. The conquerors always treat the conquered shabbily. So while the British-Americans did things differently than what has been done through most of human history, I'm not going to say that it ended up being more beneficial. However, many of the cultures, and some notion of self-governance (again, as reaffirmed by the Supreme Court this morning), survived.