Rapid population decline
increased violence toward outsiders
collapse of traditional social structures
abandonment of traditional belief systems
what does this list describe?

The above list describes a state of warfare.

Explanation:

When a state is at war, its population is deemed to decrease out of the poor living standards due to war-time expenses, deaths out of disease outbreak and also out of war.There is also collapse of traditional social structures in the times of war to come up with structures for war.Traditional belief systems during the time of war are secondary issues that people no longer give interest in.