Genocide Poison

The Genocide Poison is an unknown substance that Bongo possesses, capable of rendering all Gerudo women incapable of producing male offpring.

Rise of Ganon
Bongo gives Ganon the genocide poison to pour into the Gerudo's oases after they deny his request for an alliance, supposedly to force them into an alliance later in exchange for a cure. In reality, she intended simply to wipe out the Gerudo race as a future threat upon obtaining the Triforce.

First Golden Age
Due to the effects of the poisoned Oasis, the Gerudo people produce less new males with each generation, until by 71 AG, Ganondorf is the only known male Gerudo to have been born. With dwindling populations and resources, they are forced to ally with the traitorous Sheikah Agahnim in hopes for a cure, and imitate the Gerudo Wars in 99 AG.