The Whole Timeline Of The 100 Explained

Six years later, a mysterious ship appears in Earth's orbit. Members of the 100 investigate and discover it's a prison colony transport from before the first apocalypse. The prisoners took control of the ship on their way to a space mining outpost, but the damaged vessel lost the ability to travel quickly. The prisoners entered into cryogenic sleep and set a course for Earth.

Back on Earth, the bunker has devolved into a ruthless place torn apart by competing factions. One clan leader has taken control of the bunker's food supply and left the other 1,100 inhabitants to starve. This leads to a revolt by the other 11 clans, who now call themselves Wonkru. They take over the bunker and work on finding a way back to the surface.

On the surface, Clarke has discovered an untouched valley. There, she finds a feral child she comes to raise as her own. Clarke is captured by the prisoners after they land on Earth, but freed in an exchange with the Ark's colonists.

The Wonkru make their way out of the bunker and rush to the untouched valley to begin their new civilization. While they initially hold the valley for themselves, they come to align with the Ark colonists against the prisoners from the returning spaceship. A war breaks out between the two sides and the prisoners bomb the valley, destroying the last bit of inhabitable land on Earth.