Conditions of sustainable civilizations

Theses on the conditions of sustainable civilizations

1. Sustainable civilizations manage to keep their population within limits, having neither growth nor decrease in the very long term
2. Sustainable civilizations do not consume anything. They use what remains available and what is replentished at the same rate
3. Sustainable civilizations manage to contain internal threats (e.g., conflicts) from reducing their population below critical lower limits or impeding its ability to pass on knowledge
4. Sustainable civilizations manage to avert destruction by external threats (e.g., asteroids, averse climates, reversal of magnetic poles). This would seem to require significant technical capabilities

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