I can cite two examples:

- Strictly religious cultures limits access to sex, and are more prone to conflict or terrorism (think some hard Muslim groups, like Talibans). If a young man was happy and had plenty of sex, why would he want to blow himself up?!?

- Bonobos use sex for pleasure and to ease conflicts, and are a quite peaceful species among apes.

If you think about it, it's just logical: the higher the level of testosterone, the higher the aggression drive. Having sex lowers that level, so... :-)