Why did the U.S Government/Military believe that Indians must be defeated, pacified and put on reservations??
both Indians as well as Anglos had their point of view of each other what i would like to understand is what were their reasons??
The answer to your question transcends any issue of politics and governance, and lies in the age old issue of perceived Anglo-Saxon superiority. People of European ancestry for many years have considered themselves superior to those of other cultures; in fact for many years, European civilization was considered the ONLY civilization. From the beginning, Indians were considered uncivilized savages who should be pushed aside.
After an attack by Indians in retaliation for stealing supplies at the Jamestown settlement, the colonists unhesitatingly blamed the problem on the Indians:
That all men may see the impartial ingenuity of this discourse, we freely confess, that the country is not so good, as the natives are bad, whose barbarous selves need more cultivation than the ground itself, being more overspread with incivility and treachery, than that with briars.
In writing the Declaration of Independence, Thomas Jefferson spoke described the abuses of George III, including:
He has excited domestic insurrections amongst us, and has endeavoured to bring on the inhabitants of our frontiers, the merciless Indian Savages whose known rule of warfare, is an undistinguished destruction of all ages, sexes and conditions.
The government of the United States broke every treaty ever entered into with Indian tribes, usually justifying it on the basis that the Indians were "wasting" the land. One American military official in the Indian wars of the nineteenth century justified killing Indian children by stating that "nits make lice."
To answer your question, U.S. policy towards Indians in the past several centuries is a continuation of the policy towards any people who were not of European ancestry.