I think it is approximately correct to say that no industrialized nation holds on to slavery. Slaves are not productive enough in industrial and post-industrial economies.

The point of US civil war was that the industrialized North wanted to rid of slavery and the agricultural South wanted to go on with slave-dependent growing of cotton etc.

Likewise, places where formal abolition of slavery was more recent (e.g. Kingdom of SA and Yemen until 1962, Oman until 1970, etc) are hardly industrial nations.

(Yes, this is not the complete picture and things are not straightforward or simple: compare to slave labor in Nazi Germany and Soviet Russia, etc, where some of it was used in industrial-type activities, and even R&D, as described by Solzhenitsyn in In The First Circle; however, you could describe these as solutions for war-time economy, and not sustainable.)

I don't see the relevance. The point is that the US did start it's rise to power in much the same way as China: By undercutting the established industrialised base and treating people worse in the interrim. Same with Germany (undercut the British). The position of slavery today has no relevance to that: China thankfully doesn't need slavery to be able to undercut the US.