is now available in paperback. Penguin put their edition on sale last week, with slightly modified cover art and the current map of the nations.
The book is also available in Viking hardcover, Kindle, Nook, and audiobook editions. I've provided links to the Amazon pages for informational purposes, but buy them from your local bookseller if your community is fortunate enough to still have one. (Here in Portland, Maine, that's Longfellow's where there are usually signed copies in stock.)
For more on the book, try the reviews and media available from the American Nations page at colinwoodard.com.