Well certainly the slave and cotton trade was a dominating part of the early American economy.
>The average slave owner held almost two-thirds of his wealth in slaves in 1860, much less than he held in land.
https://www.encyclopedia.com/history/news-wires-white-papers...
"America was built on slavery" is obviously a bit of hyperbole, but given the economic boost to agriculture in the south built on the backs of African slaves, or the literal building of the east-west infrastructure on the backs of Chinese ones, I don't think it's an unfair claim.
Prior to the civil war, slaves were the single largest asset, by value, that America held -- more than it's land or agricultural exports; more than it's railroads, banks, or factories. Cotton was the number one export across all of America, not just the south, at that time. And it's not like this value was destroyed by the civil war -- post-slavery institutions were extraordinarily effective at restoring or keeping pre-slavery conditions long after the end of the civil war. The slaves may not have physically built most of America -- but it's silly to suggest America's wealth isn't largely, perhaps primarily, born from the fruits of slavery.
For sources, feel free to examine any modern history book.
Perhaps not literally built but built off the backs of slaves, definitely.
Where did you learn that?