> I'm confused by the argument made here. An economic system fairly different from the modern world, which was not called capitalism at the time ("capitalism" is mainly an 1880's+ idea), used slaves. Slavery was abolished and later that system evolved into capitalism.

Capitalism was a term coined in the late 19th Century to refer to the post-feudal economic system that developed through several centuries and was in full swing by the mid-19th century, and overlapped considerably with the use of chattel slavery.

While its critics hadn't yet called it "capitalism", the system which they did get around to calling "capitalism" did not evolve only after the abolition of slavery as you claim.