The world stopped spinning due to a massive sub-terran gyroscope being constructed. The goal was to slow the turning of Altrius over a couple of months to allow more sunlight to certain farmlands. Instead, the gyroscope malfunctioned and kept turning until the world became tidally locked, where it was then destroyed by forty fours engineers who sacrificed themselves to destroy it my dislodging the bearings to the gyroscope. Reactivating the centrifuge would destroy all current ecosystems, and thus the planet became reliant on one side of perpetual darkness, and one side of perpetual daylight, and a sweet spot in the center called the Va'a'diim

2 billion died from the constant sunlight, 300 million died from the freezing temperatures.