Original gene pool very poor – England’s felons & prostitutes, then further damaged by mentally deranged (believers in god), quitters (running away from their own countries instead of staying to fight for improvements) and cowards (people who accepted slavery rather than die fighting against slavers).
They stole land and infrastructure from the British and enshrined the 1776 British political and economic system in an archaic constitution before stealing the rest of their country from the native Americans and the Mexicans.
Having stolen the land they then used slavery to corner as much wealth as possible from the rest of the world. They currently have a country where the inhabitants have no care for each other’s welfare, with a dysfunctional electoral system masquerading as democracy and a constitutional straitjacket against progress.
Also the United States is only part of (North) America yet its citizens claim the unqualified name of "American" as their own - ignoring the equal rights of Inuit, Canadian and Mexican to it.