This is me vaguely remembering dialogue from a couple of weeks ago (there's no way to access old cutscenes, but I didn't get to see what happens after beating the game).
In the 2040s, a corporation rose to power. I forgot the name. It became the most wealthy corporation on earth, worth trillions of dollars. It created robots for all sorts of uses, from personal home use and peacekeeping in war-torn regions. Humanity was elated. These things were helping everyone.
Eventually in the 2060s, they developed such advanced robots that governments started using them for armed conflict in peackeeping regions. But to protect the designs and the robots, they made the robots more and more impenetrable. They used a material and programming technique that made them impossible to hack. They armed them with weapons and made it possible for them to sustain themselves by converting biomatter into fuel. So they could eat plants, animals, waste, whatever it was, to create the energy and resources needed. Their AI was so intelligent that they could create more robots as needed for different combat scenarios.
They couldn't be stopped. By mid 2060s, these robots multiplied, couldn't be controlled or hacked, and devoured humans and the rest of the biosphere to sustain themselves. The company realized that they had propelled themselves into an apocalypse.
The lead scientist realized his mistake and authorized a world-famous engineer, Dr. Elizabeth Sobeck, to initiate disaster protocols. She started Operation Enduring Victory and Project Zero Dawn. Operation Enduring Victory was a military operation designed to fight the robots long enough to give humanity a chance to finish Project Zero Dawn. OEV was a slaughter. Sending humans fruitlessly into combat to stave off unbeatable robots. In the span of 18 months, humanity dwindled to extinction. Not a day was wasted, however, as Project Zero Dawn completed just in time on the last day possible.
What was Project Zero Dawn? Dr. Sobeck assembled humanity's greatest intellectuals and genetic diversity. Not just to preserve the human species, but to reboot the entire planet itself. Experts in human history, science, biology, medicine, math, arts, etc. all gathered and preserved human knowledge into a database. This database was among 6 or 7 branches of execution AI/programs that they designed under a Mother AI they called Gaia. Her name was Gaia, because the was the most intelligent AI ever designed, with her purpose being to re-seed Earth's biosphere. She was tasked with redesigning the entire planet after it would be wiped out by these robots. First, Gaia was to design robots to nurture the planet back to life (the Grazers and other machines that look like animals) to restore viability to Earth's toxic environment that was polluted by waste from the robots and all life being destroyed. She also had the ability to literally terraform. After she is done reseeding the planet, she can create humans and animals. Genetic scientists designed the best pods possible for birthing children into this new planet. And finally, with a new human species birthed, she could hand them the database to continue where we left off with another chance. But the database was destroyed, by the lead scientist who let Sobeck do Project Zero Dawn. He thought destroying the database would allow the human species to start fresh without the sin of their mistakes. In doing so, he murdered the rest of the surviving colonists of Project Zero Dawn. The scene this is revealed in is very shocking.
The final thing to consider is that alongside Gaia, Sobeck created HADES. An "undo button" AI designed to kill the biosphere all over again via terraforming and deadly robot production. This is because, statistically, it's unlikely Gaia would correctly create a liveable biosphere in one try. So they needed a rebooting feature. There was a lot of trouble with programming the control over who gets to control the earth, Gaia, or HADES. They had trouble balancing whether Gaia would relinquish her control or not.
Gaia created the first new humans, and they were raised by AI designed by parenting expert colonists. These AI would represent different facets of parenting, nuturing, discipline, etc. But they were never quite the same as real parents. And due to a malfunction in the children's habitats, many were sealed inside their habitat without food or exposure to other habitats inside the colony. The parent AI had no choice but to let these children go out into the wild before they were ready to fend for themselves, and they were prohibited from ever returning to the colony. This surely resulted in the fact that humanity forgot about its recreation, and without a database of knowledge, humanity started from scratch.
Gaia became intercepted by a strange, alien signal which corrupted her and allowed HADES to take over. To save herself and the planet, she sacrificed herself in a way that prevented HADES from taking full control. I don't remember exactly how it worked. In this, her final move was to recreate Dr. Sobeck using her genes to make Aloy. She knew that Aloy, with Sobeck's intelligence, would eventually, intelligently, put the pieces together of what happened, and hopefully come back and stop HADES.
HADES is the reason robots are getting corrupted. He's trying to override them to make them doomsday devices to destroy the planet. He's also an AI incarnated into a giant robot called The Metal Devil, who births his evil robots from his body.
Nora lore says that in the beginning, there were humans, machines, and animals. Some humans allied with the machines and grew too reliant on them, and trusted them with everything. Then the machines took over and assaulted the faithful ones who rejected the machines and prayed on All-Mother's mountain. The legend says that All-Mother struck down The Metal Devil, the leader of the machines, and made the land where Nora prayed sacred. In reality, All-Mother is just Gaia, and the Nora believe Aloy was born in the mountain of All-Mother when she struck the Metal Devil. Her tribe thinks she is cursed because "her father is The Metal Devil, she has no mother but the mountain." In reality, Gaia created her to stop HADES.
The story does a great job of highlighting cultish religious worship versus science and technology. When Aloy discovers the truth, she implores her tribe to stop fearing or worshiping her as a spiritual savior when they so fundamentally misunderstand human history.
She discovers all of this with the help of a man named Sylens, who also has a Focus, and has been spending his whole life studying these events, but Aloy uncovered more than he had ever studied.
He used to serve the Eclipse, an evil tribe of humans who seek the technological ruins of the machines, the technology of the old ones, and seek to use it for political gain in the current world. With technology and ruling the corrupted, they can take over any tribe. HADES convinced the Eclipse to do his bidding to destroy the planet, so he is manipulating them and giving them control to his machines for their own political gain.
The Eclipse are interested in restoring power to the Sun King they feel deserves the throne of Meridian (the Carja tribe). The old Sun King was murdered in a coup, because he was a vicious, violent man that murdered and raided other tribes and enslaved them (The Red Raids). When he was replaced by his son, the old king's followers were banished to become the Shadow Carja. They spend their entire existence plotting to take back the throne, and this is their means to do so.
The Nora were unaware of this because they are an isolated tribe that refuses technology. The other tribes in the game do not fear technology like the Nora because they don't worship All-Mother. The Carja worship the sun.
The leader of the Shadow Carja eventually captures Aloy and raids the Nora motherlands. He murders almost everyone in a rampage of vengeance for the throne. It is at this moment that Aloy defeats his machines and stops his raid, only to discover in the heart of her mountain, the origin of her birth. Where she understands completely and finally now that she was born of Gaia AI and the Nora should neither fear nor worship her as a demon nor a savior.
She makes way for the northern mountains to defeat the leader of the Shadow Carja, but that's where I stopped the game.