In order to avoid problems with the Native Americans, the federal governments decided to gradually assimilate the native population into the American society.
There were multiple actions taken to accomplish the assimilation.
The Native Americans were granted all the rights as the other people, which enabled them to constantly communicate with everyone else, to get familiar with the culture, and get exposed to the culture, eventually accepting it.
Also, all the Native American children were obliged to visit school and get educated. The education was on English language, and the children were mixing from early age with children of the other ethnic groups, thus becoming Americanized from very early age.
They were allowed and motivated to work in the places were everyone else was working, which led to further assimilation, as the majority of the people were not Native Americans, so in order to fit in they had to merge into their culture.