Anglo-conformity is the desire of people in power to impose their ordering of the world upon another group. It is best to view this idea from a sociological point of view.
All cultures have a different understanding of the world. To put it another way, all culture have their own commonsense view of the world. To be more specific, each culture has it own view of family, religion, happiness, transgression, and the list goes on.
In light of this, when cultures come together, there can be conflict in many ways. In other words, whose view of the world will win out? Rarely is there a peaceful mixing. Anglo-conformity is the desires of people of Anglo backgrounds to impose their worldview on others - the Native Americas, in this case.
The Native Americans resisted in many ways. Often they held onto their political structures, religions, and views of family, to name a few. They even fought many battles to retain their culture.