I have heard for 35 some years or more, that American history books where revised, and changed in the 1920's to what is read now by school students. My son is a major American history buff, and i would like to get him an American history book that was written before American history was changed (if it was?) Any recommendations on what title, and where to buy one? I am not looking for a collectors addition, a fairly good shape used text book would work out fine.

These are the sort of books that are being thrown out at home and removed from library collections all over the country.

Try a used book store--those are going away, too.

Ebay or Amazon, especially if you have the ibsn.

If you like digital books, Project Gutenberg is your source. They have over 1000 books of all types digitized, and they are almost all public domain, over 100 years old.

My favorite historical topic is the first world war.  I collect and read everything I can get my hands on regarding the topic.  Used booksellers, the creepy firetrap places, often have that kind of thing and it's been sitting around long enough that they're usually grateful to see it go.  

One thing I will say though is that the books written on ww1 during and immediately after the war were CRAP.  The propaganda machine was in high gear at that time and the "histories" largely consist of that sort of thing and a lot of glorious backpatting.  It's interesting though to trade today's skewed viewpoint with yesterday's skewed viewpoint.

Check garage sales, small variety stores or trade/flea markets as well. My dad found a 1938 edition of Encyclopaedia Britannica for $35 at a garage sale, complete with the small shelf that it came with. I've only skimmed a few volumes, but it's absolutely fascinating reading.

Second hand book stores.

Try Abe Books. ABE Books

http://www.archive.org Has everything you seek.

This is one of my favorites. A History of the United States for schools and academies published 1839 by John Frost

I have purchased a few old history books from the early 1900's and the 1800's from eBay.  They aren't very expensive if the condition is rough.