Obviously the answer to this question is not going to be a single factor. If anyone tells you that there is a single-factor explanation for societal collapses, you know right away that they're an idiot. This is a complex subject.
这个问题的答案显然得从多方面考虑， 如果有人告诉你：“这些社会会崩溃，只有一个方面的原因。” 那么你应该马上反应过来， 这人是个傻子。毕竟，这是个非常复杂的问题。