In the middle of Act 1, to get access to the sunken temple, you have to go in the field where the Nephalem, if I understand it well, killed each other until there was not enough to continue the race. Their ghosts were still fighting in that very field.
But what triggered that "Civil war" of the Nephalem? What happened to make them start to kill each other to a point where their species just disappeared from Sanctuary?
