Two factors that are seldom mentioned:

1. Modern people make worse parents in many respects. They might be more caring, when they actually have children, but they have less time for children, and are more distracted by other aspects of life. And overall, the general perception is that their commitment to family is much looser than in times past.

2. Standards are simply much higher than they used to be. People don’t want to have children with whomever, and they want their children to be successful compared to their peers and that’s not easy to achieve and failing that, they’d rather not have any at all.

A lot of their success is due to their tactic of rushing into the enemy without any care for supply lines and logistics. This often worked to their advantage but most of those early wins were not sustainable in the long run. It gave the impression that they were more powerful than they actually were.