Tom Woods says so in “33 Questions”. I would be interested to see how that calculation was done. Somewhere I read the war cost the US Government the equivalent of $84 billion in today’s deflated dollars. Where has the value of the slave workforce been calculated?
The US Government spent over $6 billion on the war, and the CS Government spent over $2 billion. There were approximately 4 million slaves, and the mean value was approximately $800, which means their total value was about $3.2 billion–far less than was spent on the war.