If you are referring to the Indian Termination policy, then the purpose was to eliminate the special laws/privileges that Native Americans had under the current government structure. Instead, this policy was focused on full assimilation into American society/culture.
Throughout the 1950's, several laws were passed in different states in order to move Native Americans away from tribal sovereignty (aka the ability to self rule) and were more focused on making Native Americans citizens who followed state and federal laws just like all other citizens.
However, due to increased activism during the 1960's, many of these laws are taken out of American society and several native tribes regain their sovereignty.