Let’s see:
Orcs - Lost many in WC1 and WC2, then split into New Horde, Dark Horde, True Horde and Fel Horde. We roflstomped the Dark Horde, True Horde and Fel Horde.
Trolls - The Darkspear tribe was tiny to begin with, and Murlocs almost exterminated them in WC3. (lol)
Tauren - Almost exterminated by Centaus in WC3. (lol)
Undead - They can’t reproduce, and both Horde and Alliance just killed a lot of them fighting against Sylvanas.
Blood Elves - 90% of the original High Elf population was exterminated by Arthas, with the remaining 10% splitting into 9% of Blood Elves and 1% of High Elves. After that they lost a lot of people in tBC and Mists of Pandaria.
Goblins - Their island exploded. Those who didn’t die in their island were caught in the middle of some shady alliance naval operations to capture the guy that was saving the world. Many drowned at sea. Many were killed by the Alliance. The survivors of all of that explode on a regular basis.
Pandaren - While the neutral population of Pandaren in Pandaria is quite healthy, the playable population is the Wandering Isle Pandaren, AKA the students of a Kung Fu school on the back of a turtle. Half to each faction. That can’t be a big crowd.
Nightborne - The entire Nightborne Race lived in a single city, and that city just went through civil war, with many dying, many withering and many joining the Burning Legion.
Highmountain - With the Bloodtotem joining the Legion and the Drogbar destroying entire villages with a single swing of a Titan Hammer, the Highmountain population was considerably reduced throughout Legion. They are probably the least genocided Horde race though.
Mag’har Orcs - We roflstomped them so much on WoD that all their Clans crumbled and their entire race turned into a single clan. Think of that the next time you get into a canon and kill 1000 Orcs at a time in Draenor! The fact that Gul’dan corrupted many of them in HFC didn’t help.
Zandalari - Zandalar is big on the game map but on the canon map it’s super tiny. They can’t be many. They don’t even live on the whole place, only on a third of it. The Cataclysm also hit Zandalar so badly that they were convinced that they would all die if they didn’t take over Pandaria to live there. Their proud navy was exploded by Gnome bombs.
https://static.wikia.nocookie.net/wowpedia/images/4/4e/Chron3_map_of_Azeroth_after_the_Cataclysm.jpg
Vulpera - Almost exterminated by the Faithless Sethrak. The Alliance sending Warlocks to set the Vulpera on fire didn’t help.
Humans - Of the 7 original Human Kingdoms, only 4 are left. We will discount 2 for being their own separate “Races” ingame. So only Stormwind and Dalaran left. Stormwind was destroyed in WC2 and rebuilt later, while Dalaran was destroyed in WC3 and rebuilt later.
Dwarves - Probably the least genocided Alliance Race, they’ve been through a Dwarf civil war 200 or so years ago that took it’s toll. The Bronzebeard were also brutally sieged in Ironforge back in WC2, and large populations of Wildhammer were destroyed in Cataclysm’s Twilight Highlands.
Night Elves - Remember the War of Thorns and the Burning of Teldrassil? It happened pretty recently!
Gnomes - Almost exterminated by Troggs and radiation pre-vanilla.
Draenei - The entire Draenei population had to fit inside the Genedar, the Spaceship in which they arrived in Draenor (now known as Oshu’gun). Then they were genocided so badly by the Orcs that they used Draenei Skeletons to pave a giant road that leads to the Dark Portal. After that, many of them degraded into the Broken and Lost Ones. Probably the most genocided playable Race.
Worgen - One of the human kingdoms we discounted earlier, many Gilneans were killed by Feral Worgen. Then many more were killed by the Forsaken and their Plague that made the land uninhabitable. And there was also the Cataclysm taking chunks off the nation in real time with the then brand new World of Warcraft Terrain Phasing Technology!
Void Elves - They were a single small research team partially consumed by a Void Ethereal. It’s hard to even call them a population.
Lightforged Draenei - They were always a small population fighting an uphill battle against an infinite army. Then their single spaceship was destroyed (good thing we were around with Velen’s spaceship! They’re still squatting in there lol), with many dying. Many also died right in front of us in Argus and Antorus.
Dark Iron Dwarves - We killed lots and lots of them in Vanilla and Cataclysm. We even killed their king. And there weren’t many of them to begin with because 200 years or so ago they exploded their own mountain summoning Ragnaros the Firelord. Said Firelord immediately enslaved the ones that didn’t die outright.
Kul Tirans - Like Zandalar, Kul Tiras is also “lore-tiny”. And 3 of their four Houses turned on them, with the Drustvar guys joining the Drust, the Stormsong guys joining N’zoth and the Ashvane guys doing evil capitalisms. Their proud navy was also obliterated when they all fell into a hole in the ocean.
Mechagnomes - Like, they all lived in a single yard when we get in there. Most Mechagnomes had been fully transformed into lifeless robots by King Mechagon and only a small resistance remained.
I’m fairly sure all playable races are on the brink of extinction. Azeroth is a weird place lol
I’m sorry!