For the Draenei, see the
Path of Glory, a road paved with the bones of Draenei. The Orcs were merciless to the Draenei on the world they shared. The Draenei can forgive a lot, and have allied themselves with the Horde to defeat the Burning Legion many times, but on a personal level it may be hard for Draenei who have suffered genocide to put it past the Orcs - even if they were corrupted by demon blood at the time. Eredar who gave into the Legion and suffer demon blood may be less sympathetic to these atrocities unrelated to them, and they may even condone or relish in the Orcs' old decimation of the fleeing Draenei who didn't bend the knee to Sargeras.
For the Tauren, see the desecration of their ancestral lands by the Dwarves in Mulgore, and more recently the Alliance's massacre at
Camp Taurajo specifically cited as being done by a firebombing by the Wildhammer Clan, which resulted in the rise of the Great Gate that closes off Mulgore. The Stonespire tribe was also wiped out by by dwarves of Bael'dun keep. The tauren see the Dwarfs' digging as hallowing, scarring, and defiling of the Earth Mother (
1,
2,
3). Back during the War of the Ancients, Desdel Stareye regarded the Tauren as barbaric and uncivilized, though in more recent times Varian recounted that the Tauren were the only ones among the Horde that didn't make him want to draw his sword. While the Humans seem to get along well enough with Tauren in general, and the Tauren have a steady relationship with the Night Elf sentinels after the War of the Ancients, the dwarves keep ruining relations with the Tauren over and over again.