6 ideas
When the Moon fragments, the pieces will progressively collide and multiply until they rain down as a bombardment that sterilizes Earth's surface for thousands of years. A precise, calculable countdown to extinction transforms an abstract threat into an engineering problem with a fixed budget of time, forcing every decision to be optimized against a known terminal date.
When a population collapses to a handful of survivors, random genetic drift would normally doom the descendants, so reproduction must be deliberately designed rather than left to chance. By having each surviving woman intentionally select distinct heritable traits, a viable diverse species can be reconstructed from a near-zero founding stock through conscious choice rather than natural selection.
The Swarm faction breaks from the central Cloud Ark, driven by a charismatic politician and by voting and messaging among frightened survivors. Their decisions, made on persuasion rather than engineering analysis, lead to starvation and cannibalism, with the collapse of order ending in the loss of nearly the whole population. When survival hinges on physical margins, governance that favours popular persuasion over technical judgement can kill everyone who follows it.
When a population passes through a tiny genetic bottleneck, the deliberate choices and personal temperaments of a few founders get fixed into the lasting traits and stereotypes of whole peoples. Each Eve's decision about which traits to engineer, such as aggression, cleverness, or deferential calm, produces a race whose social role is predictable millennia later. The bottleneck turns individual preference into collective destiny.
Treat physics, not character intention, as the main antagonist: delta-v budgets, propellant, radiation, and debris-strike probabilities decide what survival strategies are even possible. Seen this way, many human conflicts in a crisis are disputes over how to spend a fixed, non-negotiable resource budget, and heroism consists of finding a manoeuvre the constraints still allow.
They agree that each Eve will use parthenogenesis and genetic engineering to found her own lineage. Five thousand years later these seven races, each shaped by its founder's choices, are the organising structure of a space civilisation of three billion people.