The Romans used the silphium plant for birth control. They weren't trying to have kids but couldn't, they were trying not to. It's a natural course of societies, once all danger has been removed people start getting more and more hedonistic, it hits the upper class first but eventually it filters down to everyone. The upper class gets replaced from lack of heirs but the structural problem remains (too much wealth, no danger nor any great mission) so they fall prey to it too.