A collapsed society may revert back to a more primitive state, it could become apart of a stronger society, or completely disappear. When societies get absorbed it is almost impossible to erase the cultural aspects that come from these societies, so when civilisations collapse the culture is likely to adapt and be carried on in a new stronger society where as when a civilisation disappears it is known that they often just leave without a trace for example this happened with the Harappa civilisation.
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