Drought

The Jungle was dying. Drought had stricken the land in which you and the Dark Trolls lived. It had been dry for two years and most of the plants and animals had died or moved on. The last of the lakes nearly dry. The humans under the rulership of King Fredric had access to wells that tapped into water deep underground. Something had to be done.

The Dark Trolls had a choice, reveal their existence to the humans, once and for all proving that they existed and ruing the safety that ambiguity gave. This would gain them access to water and allow them to say in their home.

OR they could leave their home, keep their existence a secret and find a new place to live and more importantly drink.