According to Joseph D. Unwin who 1934 published a book called "Sex and Culture" dealing with the correlation between a society's level of "cultural achievement" and its level of sexual restraint.

His study of 80 cultures throughout history led him to the conclusion, that as cultures/societies develop, they become more sexual liberal, which leads to a loss of cohesion, impetus, and purpose. What inevitably follows is the succeeding decline of this culture/society.