Can't blame the US for the slavery of mankind.
The US is not the be all end all of slavery.
The left uses slavery as a way to delegitimize the United States.
However, they never provide any context. As said, slavery was a worldwide practice that predated written history.
So, by the leftist criteria, the entirety of civilization is illegitimate, including Africa. You can make a case that Africans were even worse for selling their own people down the river.
http://www.discoveringbristol.org.uk/slavery/routes/bristol-to-africa/trade-goods/slave-trade-goods/A ship going to Africa to buy slaves carried a large cargo of mixed goods, such as cotton, brass pans and guns. These were exchanged for enslaved Africans, who were shipped across the Atlantic Ocean to north and south America and the Caribbean. Here they were set to work on the plantations (large areas of land owned by Europeans where crops were grown). The ships’ captains would buy goods to take back to Europe. These would be goods produced by slave labour on the plantations. They were tobacco, sugar, indigo (a plant used for dye), rice, rum and cotton.
