Most books in Tripod will have subject headings assigned to them. These subject headings can be helpful for identifying what a particular book discusses substantially, rather than just tangentially.
When it comes to subject headings, you'll only find a particular book in the most specific category that has been applied to it. So if you browse the list for Peasant uprisings > Mexico > History and Peasant uprisings > Mexico > History > 20th century, you'll find two entirely different set of books that don't overlap.
Here are a few different ways that subject headings can be applied to books (there are many others!).
Books discussing a topic in a particular country