This is one I remember starting and for some reason I never finished some years ago. I found it in the attic recently when I was sorting books.
This book was very good and I have absolutely no idea why I never finished it first time round. This is classic Card, with some clever plots, woven into a science fiction story that is creative and original. Like so much of his work, religion plays a central role in this book - but this is not a religious book itself. As usual Card has done his homework, and there is plenty of the history of Christopher Columbus here, as well as some other interesting ideas about Noah's flood and such like.
This is both history and alternate history, as people in our own future look back on the lives of people in the past using a machine that allows them to spy on the past. In this future world warfare has at last ceased - mankind is at peace and projects are underway to fix the damage we have done to our world. Meanwhile the Pastwatch historians look regretfully at all the evil mankind has perpetrated to get to that point. One event seems to be especially cataclysmic - the voyage of Christopher Columbus to find the shorter (sic) westward passage to the Indies (Asia).
As usual, one could pick a few holes in the science and such like - but not for any good reason. This is an intelligent novel from Card when he was at his zenith. Sadly his most recent books have not always been up to this standard, but this one is most definitely worth a read.