History of Goblinoids

Goblinoids were created during the reign of the Tomb King to feed the hordes of Undead armies.
The Tomb King created goblinoids from his prisoners for food. Each humanoid was corrupted and turned into some form of goblinoid. Halflings, Gnomes, and Dwarves became variations of Goblins, Humans became Orcs, Elves hobgoblins, and Firbolgs became Ogres. They were created as low intelligent evil creatures who could be easily controlled.
Many of the halflings and gnomes were not corrupted and maintained their benevolent nature. These goblins lead a resistance and escape networks. Though few succeeded or survived their attempts to escape the horde, enough did and found hold outs of demihumans and eventually joined the great army destined to defeat the Tomb King.
After the final battle and the crushing defeat of the undead horde the freed Orcs, Goblinoids, Bugbears, and Orges fled but many of them were "gentled". Wizards and clerics worked together to undo the corruption of the tomb king and those who were "cured" became the playable half-orcs.
It was learned that only first generations of the corrupted could be cured in this way. This created 2 versions of of Goblins, the gentled version that live among civilization and the monstrous.
The gentled races retained many aspects of their monstrous captive ancestors including language and some customs. Some of the gentled versions fled with their monstrous kin feeling a connection they could not leave. Therefore as a player of any monstrous race your origin could be from either a civilized descendant living for generations among the demi-humans or they could be a defector from a savage monstrous clan. Many formed their own barbarian societies just as other demi-humans did.
All of these races, half, whole, savage and civilized draw their ultimate origin to being created from demi-humans corrupted by the Tomb King.