Why did the government adopt a policy of Americanization

At the start of the twentieth century there were approximately 250,000 Native Americans in the USA – just 0.3 per cent of the population – most living on reservations where they exercised a limited degree of self-government. During the course of the nineteenth century they had been deprived of much of their land by forced removal westwards, by a succession of treaties (which were often not honoured by the white authorities) and by military defeat by the USA as it expanded its control over the American West.

presidency should be the title

the answer is a new goverment.