The resurgent claim that the modern economy was built on slavery is yet another attempt to attack capitalism while also claiming "we are all to blame" for slavery. The slave owners of old tried a very similar tactic.
It is troubling that after a decade of an economic expansion, the US government is still spending money as it does during and immediately following a recession. It is as if the economy is now in a state of permanent "stimulus."
The United States is not a nation. From the very beginning it was more of a collection of various nations united by ideas of political unity and by fairly high levels of tolerance for other groups within that union. The US certainly contains nations, but it was never a single nation.