Why did the government wanted to eliminate American Indian languages and cultures?

It was thought that inner communications would threaten government overthrowing and taking back of land. As well, when you weaken a group of people and oppress them, they can become easily scared and subservient as a result of their fear. If they cannot speak their own language any longer, they are forced to assimilate into the society your country is wanting, and disconnects them from the land and ancestors, forgetting the reasons they should fight to keep their connections and languages.  Unity can become forgotten in times of turmoil, furthering the point many will be scared and unwilling to fight without many allies.

i beleive a. is the only possible answer

he believed that strong monarchies would lead to social and political stability.