I'll give you another just as likely reason for past societal collapses (frankly, a lot likelier reason), and you can then fill in more if you are able. In times of peace, leaders have no dire motivation to mold their citizens into specific paths that are catalyst for military purposes. This leads to societes that are directionless. Historically, only military societies prevailed because they had direction and motivation to improve. However, what's so bad about being directionless? What exactly causes the downfall of "peaceful" (=actually just directionless) societies? We have to dig a little deeper. You jumped the gun and proclaimed it was peace itself that was doing the damage. That sounds ridiculous doesn't it? Peace itself has millions of little and big effects on society. Among these effects is the loss of need for children, therefore inevitably marriage laws get relaxed. Humans want to have sex a lot and with many other people, and marriage gets in the way of that. In peaceful times we have seen a gradual destruction of marital laws. This leads to marriages which can be formed and destroyed at the whim of any person, and in our society today, it's even worse because women are considerably favored in the break-up. This leads to people being very cautious to form deep bonds, and this ultimately leads to a weaker society, a society devoid of the ultimate motivation for every human being: Providing and protecting your family. It's like taking away one of the primary engines of a spaceship. There is still other engines that powers it: Need for food. Need for sex. However the strongest one, the motivation to protect your own children is gone. Because there are no children, because there are no marriages, because marriages are nowadays too fast and detrimental for male parties. What we need, is actual equality between the genders.