In the ancient ages when the humans reigned over Minecraftia and the mobs where hunted down. 
The End was still only a mith until a group of mages knew as the Arcaneus created a portal to the mythical dimension. 
They thought there could be new incredible resources that would help the mankind. 
They thought wrong, the inhabitants of the dimension was aggressive and hostile, some of the explorators were kidnapped and with the portal open the creatures could reach the Overworld. 
The humans that got kidnapped got infected by the dimension itself turning in strange abomination between the Endermans and the Humans, these abominations were hostile to everything that lived in the Overworld, there were many of this Abominations,

the EnderXplorers or Enderscouts weren't less common than the warriors but hard to see due to they clocking ability, this four eyed hybrids were capable of teleports and the special armor they weared was not intended to protect the Ender but the energy that flow through it had the unnatural and still unknown ability to disguise the Ender, even when it was close it was completely soundless and invisible, these guys were the nightmare of every human guard they usually carried shortbows and iron swords, they were deadly but once saw they were easily to kill since most of their body was bare and exposed to arrows or swords, unlike warriors they were intelligent but often fell into an animalistic fury after seeing a human's eyes, mostly like normal Endermans

a war raged and both factions destroyed eachother, the remnants got then deleted by time. 
Only few things survived such has the Stronghold which was preserved by the arcane powers of the portal, the humans got almost completely wiped out except for remoted villages and few survivors scattered around Minecraftia that tried and still try to rebuild the ancient empire which was Minecraftia. 
The End didn't did anything better, all the Abominations died and only the Endermans remain them too scattered around Minecraftia unable to return to their homes due to the portal being closed, it's told that a human would be..strong enough to mix the arcane powers to create keys to open the portal again and kill the mind behind the End once and for all.