This article is from the Paper Money Collecting FAQ, by Bruce Giese firstname.lastname@example.org with numerous contributions by others.
After the US Civil War (1865-1935), the US government created
charters for private banks to print paper money which was backed
by the US Government. There were a very large number of national
banks chartered from all over the USA (e.g. Nashville, Tennessee;
Key West, Florida; Bismarck, North Dakota; L.A., California).
Many people collect "nationals" and the prices have gone up
substantially (to around the 150 dollar level on average).