The entire way their legs and hoofs are built. They’d have paws with massive claws and massive legs. They’d run more like a big cats.

Man I wish we had shittywatercolour here to draw this up.

Horses are known to eat small animals. There's a video floating around of a horse eating a chick (baby chicken).

Since they would be predators, their eyes would be positioned on the front of their skulls instead of the sides for better stereoscopic vision, and they would likely have sharp incisor teeth. Those 2 things alone are pretty creepy.

That would make it significantly more expensive to raise and stable a horse, making them unsuitable for labor or war for all but the most wealthy, and even then it would be a dangerous prospect to raise or ride one, as we are made of meat. Other animals like oxen or elephants would probably fill this void, and lands with climates that support them would become far more valuable. Overall there would be a lot less energy available to pre-industrial people and travel over land would be a lot more difficult.

Plains nomads probably wouldn't exist or would lose their historical advantage. The Huns, the Golden Horde, etc., probably would not have risen to prominence.

Carnivorous Ungulates did exist in the past

If horses were obligate carnivores, they probably wouldn't have been as readily domesticated. It's cheaper to feed a plant-eater than a meat-eater. Dogs are omnivores, for example, because human scraps are often plant-based so it was an advantage to be able to eat more plants than a wolf might have.

And if horses weren't domesticated, that would have changed the development of technology and warfare massively. We might have still had the wheel from the potter's wheel, but things like carts and chariots might not have developed and spread like they did if one of the main animals to pull carts was not domesticated.

The way the horse and stirrup changed warfare also would have made ancient war very different, as there'd be no sudden incursions of horse-mounted warriors invading various regions at various times so I bet a lot of national borders in the modern day would be quite different.

Large animals that were difficult or costly to domesticate (like the Aurochs) were generally just wiped out.
My guess is if horses were carnivores they would be extinct or limited to a few in zoos and some of the wilder places (like tigers).

That one person you know who absolutely loves horses would be a lot creeper

Are you asking if I'd watch that movie? Because the answer is 'yes'.

Watch LotR to see ridden carnivores.
I don't know, how would the world be different, but to spark your fantasy, imagine horses being herbivores, but turn carnivorous at every conjunction of Jupiter and Saturn (~ every 20 years).

Farmers would complain about their chickens getting eaten.

We would be riding cows instead.

Horses would probably be dead or endangered if they were more trouble than they were worth.

I read that as cannibals imao. I would imagine in a world like that there would be shows where horses would face each other to the death in a battle and eat the loser in front of everyone.

I'm too busy imagining getting run down by a teeth-gnashing Clydesdale and pissing myself to answer the question

Please send help. 🧠