In the Shadow of Paradise
They came in 2400.
Humanity had just united and built up an anti-asteroid system on the moon and created a number of platforms. A colony had been established on Mars, but was retrofitted for long range, anti-asteroid detection. We were ready for something big, but not this… They came without warning, and attacked without warning. Their mission was clear: Genocide.
We later found out that they came for our resources. While we had been running out of important things for decades, they needed nuclear metals for their reactors – thorium, uranium, plutonium. The Gregori Consortium didn’t care – they wanted it all.
The war was devastating. Most of humanity was killed during orbital bombardments, and more were killed as wreckage fell from space onto the blasted earth. They were drive off, but the costs were great. Most of the Earth had been reduced to a poisoned wasteland. Our home planet could no longer sustain us. Mars was too small and too fruitless. We needed to move on.
The anti-asteroid defense platforms were used to make massive colony ships. They were designed to carry millions of humans – enough to seed an entire planetary population – in cryogenic sleep. the ships were designed to be run by AI, a semi-autonomous robots with a quantum computing core linked into a single network, managed by a single Captain. The ships were designed in modular construction, letting themselves be turned into a small, thriving city once they have landed.