I think you are confusing communism with capitalism... The nations that at any point had slavery, were capitalist. Capitalism itself can only exist in "surplus value" scenario, meaning someone/thing is being exploited.
abject poverty, only exists because abject wealth exists. Abject wealth is a result of capitalism.
You're wrong. And missing about 5 thousand years of history.
"abject poverty, only exists because abject wealth exists"
Yes, that's why the "leaders" of North Korea are abjectly wealthy. Like the leaders of Romania, for example.
Well, they certainly weren't communist, in any case. By definition slavery cannot exist in an actual communist society, since such societies are completely classless and the only form of ownership is common.
If you want to include feudalism in there I'm happy to have the discussion on what feudalism is closer to: Communism or Capitalism.