Aemon plague

Aemon plague was a fatal disease on the planet Aemonus. It is unknown whether the plague was a byproduct of a military program, or a biological weapon that was released by mistake. But the effects of the plague drastically changed the entire population. Only just the men was hit by the plague that was a retrovirus affecting Y-chromosome, and the plague caused uncontrolled aggression and permanent brain damage in any of the affected. As soon became the entire male population of Aemon Aemonus violent and psychotic who threw Aemon society into chaos.

They struggled to find a cure, but eventually discovered that the plague was simply incurable. Thus began the entire male population of the planet slowly die out.