Battle Cry of Freedom mentioned that prior to the Emancipation Proclamation, Lincoln offered to compensate the rebelling states 15% of the total value of their

Battle Cry of Freedom mentioned that prior to the Emancipation Proclamation, Lincoln offered to compensate the rebelling states 15% of the total value of their slaves (also hinting that this was better than not getting anything should they wait longer). The South rebuffed this offer. I don't think the book discussed how he landed on the 15% figure. My guess is that the number of slaves was so great that 100% compensation would be more expensive than the cost of seeing the war to its end.