Tales of the Borderlands
Dragonborn are the descendants of an ancient empire called Arkhosia.
Razortear: one of the last stands of the dragonborn, with more than ½ million tieflings laying siege to the dragonborn for more than 10 years. The tieflings dug a huge tunnel to win the battle.
Hobgoblins once had an empire in which bugbears and goblins were their servants. This empire fell to internal strife and interference from otherworldly forces—perhaps the fey, whom many goblins hate.
Vumerion was a legendary necromancer that had a tower called the Black Tower of Vumerion. This was the origins of the first Skull Lords.
One hundred years ago the Nerathian Empire fell to infighting and the hordes of the Ruler of Ruin. Their old cities and castles mostly lay in ruins.