The right answer is poverty. After visiting and working in prisons, asylums and almshouses, among others, Dorothea Dix witnessed that people with mental illnesses that were confined in those places, and treated badly, were also very poor. In fact, in 1854 she even presented before Congress a Bill for the Benefit of the Indigent Insane, which proposed the provision of federal land and funds for the creation of new mental institutions.
The federal government of the United States has never referred to its territories as an empire, but some commentators refer to it as such, including Max Boot, Arthur Schlesinger, and Niall Ferguson.