Used bookstores should still have old copies of history books...
Oops. I hit “post” too soon!
thriftbooks.com is my go-to site for used books at great prices. Seems like they have every author & almost every title— history, politics, classical literature, philosophy, science, poetry, children’s, pop culture, etc.
Also, at https://www.gutenberg.org/ebooks/
you can download thousands of the foundational works of western civilization.