An intriguing drop

Q points to historical revionism:

Buy a history book published 20 years ago.
Buy a history book published 10 years ago.
Buy a history book published this year.
Compare.
Focus on WWI/WWII
Something ALARMING will be discovered.
Q

Since I tend to read history books published prior to WWII, my library is not a good source for working out this one. Anyone have any ideas?