According to the December 2012 report by the U.S. Treasury Dept., out of the $450 million Greenbacks issued during the American Civil War, there is an estimated $239 million still outstanding.
In 2013 dollars, this would be at least $10 billion, according to this inflation calculator. While not significant today, it’s significant that such a huge percentage of the Greenbacks are still in circulation, given that they were ordered to be taken out of circulation in 1971, so there have been many that are being privately circulated or collected.
While there were $500 million in interest-bearing bonds that were issued as backing for them, the money supply grew by a total of $950 million, and the interest-free Greenbacks provided significant funding for the Civil War, when the total debt was $2.7 billion by 1865, and no interest was due, nor will ever be due, on the $450 million issued, and nothing is stopping the U.S. government from returning to directly-issued interest-free currency, other than lack of political will.
As for the validity of the American Civil War, I have publicly stated on my radio program and in a recent public presentation that the States had the right to secede from the Union, and that President Lincoln and the Union were in the wrong. The effectiveness of the Greenbacks, and of any interest-free currency, is something that can be independently judged.
For more on United States Notes, see my articles:
1) Gary North gives the false impression that interest-free United States Notes are no longer valid
2) Gary North deliberately omits the fact that United States Notes are interest-free
3) Michael Badnarik on issuing interest-free fiat money like Lincoln did: “That’d be a step in the right direction”
4) Don’t just blame Lincoln for a national legal tender law — Washington signed one, too
5) The Federal Reserve lies about United States Notes (Lincoln Greenbacks)