Pastwatch: The Redemption of Christopher Columbus

Pastwatch is a 1996 novel by Orson Scott Card combining elements of Science Fiction and Alternate History. The novel is set in a future where a past-viewing technology has been perfected, most of the main characters are historians who use this technology to observe and analyze the totality of human history. Over time, they come to see European conquest of the Americas as a destructive turning point in Earth's history. They come to the conclusion that, if they can observe the past, maybe they can alter it as well.

Card apparently planned the book to be part of a series, but the sequels (announced in 1999) have yet to be completed.

Tropes used in Pastwatch: The Redemption of Christopher Columbus include:

After the End: The world has just gone through a period of calamity that has reduced the world population to under a billion and necessitated great efforts to repair the ecology.
Alternate History: The main plot of the novel is around the characters trying to design an alternate history which they can then create. They also learn that we are living in alternate history created by beings who changed their own past.
Alternate History Wank: Given that Orson Scott Card is an observant Mormon, what else could his creation of a peace-loving Modern Mayincatec Empire that embodies an anti-racist, egalitarian interpretation of Christianity be?
Anachronic Order: Told with chapters alternating between historical fiction of Christopher Columbus and far future science fiction about the Pastwatch project. Eventually the two plot lines merge due to Time Travel.
Apathy Killed the Cat: With a past viewing device available, it seems likely that the first order of business would be to investigate every major religion, either confirming or debunking the accounts in each book of scripture. There's no mention made of this, and there are still explicitly Christians and Muslims around in this future. (This despite the fact that one character became famous by discovering the historical event that became the basis for the Great Flood).
- Presumably, doing so would result in massive riots and condemnations that the past-viewing technology is evil and is, therefore, untrue.
Atlantis: Thanks to Pastwatch (and one obsessed meteorologist), it's eventually discovered that Atlantis is the name later given to an ancient civilization at the end of the last Ice Age. It was the first civilization to organize into urban-like groups and set up (more or less) permanent structures in the Red Sea. The melting of the ice caps has resulted in the rising of the ocean levels and a destructive tidal wave wiping out the entire civilization. Only a man named Naog, foreseeing this outcome, builds a sturdy wooden boat, just big enough to hold his family and the families of his slaves. After making it to shore, he becomes a shepherd, telling the story of his lost homeland to all who would listen. He advocated two things: slavery (as replacement of human sacrifice) and a nomadic lifestyle (believing God was against cities). It wasn't until Babylon that large cities were again attempted. What all this means is that Noah was from Atlantis.
Back to Front: In universe example. One of the pastwatchers has a habit of watching the lives of individual figures starting at the end and working their way to the beginning.
The Cake Is a Lie: Despite what the politicians are saying, human civilization is doomed, as the ecological damage will not be reversed in time to save humanity from being thrown back to the Stone Age.
Dead Guy, Junior: Tagiri names Diko and Acho after ancestors she discovered with the Pastwatch computer systems and Diko's daughter that she has with Columbus is given the middle name Tagiri after her mother. Additionally, her first name is Beatrice, though her father never makes it clear which of his two beloved Beatrices he named his daughter after.
Disease Bleach: After Columbus has a near-death experience and a vision from the Father, the Son, and the Holy Spirit that turns out to have been sent by people from a previously existing timeline to create the one that led to the 23rd century setting of the novel, his hair starts rapidly turning white.
Fling a Light Into the Future: Knowing that people of the 15th century wouldn't able to understand, they left their history as a sealed record that would be found only when society had the technology to detect it.
God Guise: Hunahpu pretends to be a god in front of some Zapotec villagers as part of his plan to remake history. It helps that he's a full head taller than an average Pre-Columbian Mesoamerican.
Hitler's Time Travel Exemption Act: Averted. It turns out it is possible to change the past, but we can only speculate whether previous iterations were better or worse than our own timeline.
Incest Is Relative: Having had much experience directly watching Columbus throughout his lifetime, Diko describes him as being an older brother, father, and grandfather to her despite never actually interacting with him and later ends up marrying and having a child with him.
It Makes Sense in Context: Hunahpu sticks six needles through his penis, shows up at a Zapotec village with his bleeding and freshly-pierced junk exposed, and entreats six people to each pull one needle out of his penis and wipe the blood on themselves as part of a God Guise. Try explaining this to someone who hasn't read the book without getting weird looks.
Just Before the End: The characters realize that the earth is in the throes of an ecological upset that will probably cause the downfall of human civilization. This figures heavily into their desire to change the past.
Modern Mayincatec Empire: The Tlaxcala apparently took over the world in a previous iteration of the world's history. The people of that timeline apparently considered it such a catastrophe in the long run, they changed history (and prevented themselves from ever existing) to avoid it. A more peaceful incarnation of this is the result of Diko, Hunahpu, and Kemal's work in changing the past.
Morton's Fork: What spurs the decision to change the past even though it'll erase their own timeline and existence is the fact that things have gotten to the point where no matter what is done (other than changing the past) to remedy the situation, an even worse apocalyptic scenario than the one they've already experienced will happen, the human population will be reduced to under 10 million, and humanity will be plunged back into the Stone Ages with little hope of ever rising to civilization ever again.
Noble Savage: Played straight and averted. The characters watch the slaughter and plunder of peaceful American tribes by European invaders. This is initially seen a simple good vs. evil conquest, but they later realize that, left to themselves, the post-Aztec kingdoms would have created an even worse empire based on conquest and human sacrifice. They seek to find a way to bring the cultures together and prevent their worst excesses.
No Equal-Opportunity Time Travel: Averted. The three time travelers are a Mayan, an African and a Turk. Only one was the 'appropriate' race for that time and place. One of them intended to be killed because of his race. Of course, advanced technology and a detailed knowledge of future events can make you more acceptable to any society.
- Even the Mayan time traveler is stated to be a foot taller than the Mayans of that period.
  - This only serves to help him to pretend to be a messenger from Xibalba (the underworld).
Poke in the Third Eye: When the characters watch shamans of a Taino village, they are spooked as the shamans describe having a vision of being watched. They watch them twice, decide to do so once more, and freak out because now the shamans speak of being watched three times.
Politically-Correct History: Averted hard in that Orson Scott Card portrays everyone who is native to Columbus's lifetime as realistically prejudiced, racist, sexist, etc. for their time and it takes the intervention of time travelers from the twenty-third century to facilitate any changes in these attitudes in the alternate history that they are sent back to create.
Ret-Gone: It's clear that changing the past will wipe everyone on earth out of existence, except those who are sent. Everyone would have to accept having never existed in order to (hopefully) make the world better.
- This is also stated to be one of the reasons why Diko doesn't want to start a romantic relationship with Hunahpu and have a child that will end up being erased.
Set Right What Once Went Wrong: On a historical scale.
Teacher-Student Romance: Diko ends up romancing and marrying Christopher Columbus himself after acting as a mentor to him.
Temporal Mutability: Type 5. The characters make clear that, as soon as they enter the past, they'll begin to change it. Even contact with one of their dead bodies would introduce future bacteria and viruses into the past ecosystem, altering the entire timeline.
- There is some variety -- basically, of the events happening before the time travellers act, those based more-or-less on random chance get a "re-roll" (sailors pick random girls to sleep with), while those based on conscious and informed decision proceed roughly the same way (a ship's captain's concerns stay the same and so does the ship's course).
The Time Traveller's Dilemma: Used to excellent effect. The characters agonize over whether changing the past would make things better, and whether it could ever be justified. Even when they learn that an ecological collapse is inevitable, they're concerned about taking on that kind of responsibility. It's especially hard considering the world we're living in now is the result of time travelers from an alternate future changing their past. Whether it made things better or worse can only be speculated on.
- It's conveniently resolved by revealing that the ecological damage is irreversible in time to save human civilization.