The history section of the book price index is incredibly america-biased. History of america, american natives, japan after ww2 and vietnam in the last century.
And the irony of it is that the U.S. is actually quite history-poor, when compared to Europe, North Africa, Middle-East, Persia, China, Central Asia and India.
Historians who are not trying to sell mass market books have a much broader set of books. You won't see them in a normal bookstore.