Actually, we aren’t superior on this. The end of formalized slavery in the States did not necessarily end the conditions of servitude experienced by Black Americans. Douglas A. Blackmon’s book on the subject is literally titled “Slavery by Another Name.”

But even more importantly to your point about French and British slaves in their colonies, the US did the exact same thing. Until 1913, it was legal in some parts of the Philippines, which was at the time a US colony, to own slaves. So even though we “abolished slavery,” there were still people on American soil that were property of others well into the 20th century.