UnlearningEcon: I believe that if you read Christophe Biocca’s post [comment at EconLog*] again and carefully, you’ll find there a good reason why the argument that cotton produced on southern U.S. slave-manned plantations is unlikely to have been responsible even for the launch of capitalism. (Relatedly, the argument that I – and, I think I can say, also Mr. Biocca and Alberto – criticize isn’t that slavery was essential only to the start of capitalism in the U.S. but to capitalism in the the U.S. and Great Britain. The difference is significant.)
The fact that the industrial revolution in England was marked (and indeed furthered) by the rise of textile mills, along with the fact that much of the cotton that those textile mills used was grown on chattel-slave plantations, is a poor basis on which to conclude that slavery was necessary to spark the advent of capitalism. (Slavery is even more clearly not sufficient to have sparked the advent of capitalism.) To give reasonably sound evidence that slavery was necessary requires some sensible story for why capitalism as it emerged in Britain and in the U.S. would not have otherwise emerged (or would not have emerged with anywhere near the force or the success that it enjoyed). That an admittedly key input to an admittedly key early capitalist industry was produced largely on slave plantations is simply not strong enough evidence.
What’s the alleged mechanism? Is it that – given that all of the other prerequisites for capitalism had also happily occurred in conjunction – slavery produced a key input at an unusually low price? Again, the evidence for this claim is dubious. (See Mr. Biocca’s comment.) But even if it’s true that slave-grown cotton was, because it was slave-grown, much less pricey to textile mills than cotton would otherwise have been, that fact remains a weak reed on which to tell the story that you want to tell. History is full of instances of input prices falling without sparking an industrial take-off.
On the other side, the subsequent history of capitalism is indeed relevant to this debate. Subsequent history allows us better to separate factors that were relevant in capitalism’s early histories from factors that were not relevant. If capitalism started successfully elsewhere in later times without slave-produced inputs, this fact strongly suggests that the slave-produced inputs that were used by the earliest capitalist industries were likely not necessary for the rise of capitalism. Likewise if capitalism continued growing and flourishing without any slave-produced inputs.
So, history proves (as much as history can prove anything) that slavery isn’t sufficient to spark capitalism. And because history also provides ample evidence that capitalism can start without slave-produced inputs in places where capitalism hadn’t before existed – and that capitalism can continue to flourish without slave-produced inputs even in places where it happened to have such inputs at its inception – history strongly suggests that slave-produced inputs are not, and likely never were, necessary for the start or the success of capitalism.
* Here’s Mr. Biocca’s comment in response to another commenter at EconLog who argues that the connection between slavery and the advent of capitalism is “pretty straightforward”:
It’s so straightforward that leaders in the South believed it , much to their detriment when it proved not to matter all that much.
We don’t even need a counterfactual here. We know the price of cotton ended up much the same  after the civil war than before. The only hardship was caused by the sudden supply disruption from the South’s foolhardy geopolitical gamble. So the notion that slave labor was instrumental, even just to to the textile industry, is already on shaky ground.
Going a step further and tying it to the industrial revolution in some way is not meaningful at all.
Seems like slave labor was instrumental in building up the wealth of slaveowners and not much else. Which makes sense: at the start of the industrial revolution, all unskilled labor is cheap, slave or not.