SOLVED. Adult SciFi. A way to see the past is discovered and then a group goes back to the past to change how Columbus interacts with Aztecs. First try fails so they try again. [s]

[Tonya]

Book was read at least 10 -15 years ago.

[Ann]

Pastwatch: The Redemption of Christopher Columbus by Orson Scott Card

[Kris]

Google Books preview of Pastwatch: The Redemption of Christopher Columbus by Orson Scott Card - Ann's suggestion:

https://books.google.com/books?id=6-Q... There are different cover images.

Wikipedia's detailed plot summary - with Spoilers:

https://en.wikipedia.org/wiki/Pastwat...

[Tonya]

Solved. That's the book.