How were the Native American cultures destroyed in the late 1800's?

When European settlers arrived on the North American continent at the end of the fifteenth century, they encountered diverse Native American cultures-as many as 900,000 inhabitants with over 300 different languages. These people, whose ancestors crossed the land bridge from Asia in what may be considered the first North American immigration, were virtually destroyed by the subsequent immigration that created the United States. This tragedy is the direct result of treaties, written and broken by foreign governments, of warfare, and of forced assimilation.

Today, people see the policies of the past with 21st century eyes. One might wonder how the nation's indigenous population became "inferior" cultures in their own land, or how a nation could have committed such atrocities in the name of "progress". One might question whether it is acceptable to make national decisions without involving in the decision making process those who will be most drastically affected.