@cicerone imposter,
It is the epitome of civilisation (any lifeform). In times of abundance a creature expands in all directions.
It expands via consumption, procreation, territory, etc. With it comes increased negative by-products - Waste, overcrowding, occupational redundancy, crime, more and more.
Upon its belly it rolls, in the midday sun - Where once it hunted or foraged. Newborns frolick, their bellies bulge, 'pon more and more, they doth indulge.
Soon it needs greater horizons - And the resources cannot suffice.
It has 3 options.
1. Adapt.
2. Move on.
3. Die
1. Alter your mindset - Limit your populace - Balance resource production against demand and sustainability - KEEP IT BALANCED.
2. You can only move on while somewhere to move on to is still available.
3. Not an option taken 'lightly'