Many have theorized what they were. When the island had landed off the western United States, some had assumed they were aliens. Others believed them to be from another universe. A few thought that they were a gift/curse from God, meant to punish the people of California for not being as devout or conservative as their homeland.
They came in many colors and many shapes, but a single shape lingered: the vague shape of the common horse.
They came bearing gifts and promises, that soon were shown to be traps and lies. Declaring themselves the saviors of humanity, from humanity, they began a savage campaign to turn the world in their image, erasing everything of man if they did not submit to become the invaders themselves. To be converted, into Equestrians.
Many did, but many more refused. And so, began a war.
Given the fact that a barrier prevented man from striking, they had done surprisingly well in the conflict. The lost land of California had managed to save many of it's best and brightest, while the Canadians who guarded the evacuated Vancouver had proved to the greatest enemy of peace in the 21st century, why the greatest madman of the 20th century respected the ferocity of Canadians.
The Mormons took 10,000 of the enemy with them as they lost ground in their promised land, while the greed, deceit, and overall sin that had soaked the ground of Las Vegas had slowed the barrier down like no barrage of missiles ever could.
A last ditch effort had been put into place in the jewel of the continent's wilderness, the greatest weapons of man were charged beneath the most fearsome weapon of nature.
Should the barrier begin to take Yellowstone, radiation and lava would be combined. The barrier would absorb most of the blast, and while the exact effect of radiation in the barrier was yet unknown, lava was a different story.
Fiery death would greet the Equestrians if they advanced further. Humanity had won the planet with thousands of years of ingenuity, and millions of years of struggle. They would not give it up easily.
If they did suffer some damage from their trump card...the resulting damage from having every nation with the power of the atom attack the barrier at once with them would likely exceed it very quickly.
However, there was another. Another race who would not give up the Earth without a fight.
.......
To those brave few who wondered, many theories had been born as to what they were. Encountered in the tales of the natives and by people today, yesteryear, and likely the theoretical tomorrow, some assumed them a myth.
In black and brown, white and red, they were described. Vaguely man-like, yet quite clearly not.
Others tried to rationalize what they were. A misidentified bear. A new species of primate. A lost species of man. A few even thought them to be aliens, but they were far off their rocker there.
They were mighty creatures. Reports spoke of them breaking cars, wrecking homes, and lobbing large rocks. They ran faster than a man, and smelled more terrifying than one, and no one could quite figure out how smart they truly were.
As an assumed primate, many assumed they were smarter than most creatures.
A few even, mostly those who believed them not a descendant of the ancient ape Gigantopithecus, but a branch of humanity such as Heidelbergensis or Erectus, thought they were quite possibly beaten in intellect only by Man.
And quite possibly even Magical Horse.
....
The mountains man had once called the Rockies had been harmed by humanity.
Its creatures hunted, its trees murdered, and its minerals robbed. Truly, humanity brought only pain wherever it went.
Riding on her back, a white rabbit made a few chirps, a snide comment or two.
Landing on the pine needle encrusted ground, the yellow Pegasus looked at her pet bunny with shock.
"Angel, how could you say such things" she said in a not exclamation marked way.
The rabbit continued to speak.
"Sure.....we Ponies have cut down trees, but we've cut down a lot fewer than man has......"
The rabbit continued.
"And we....may have hunted a few monsters....." this was starting to make the Pegasus somewhat uncomfortable "Though I guess that calling something that can kill you or your livestock as monsters isn't so odd....."
The rabbit finished with a dark note.
"......I wouldn't exactly call Rarity an environmental hazard with her jewel spells....."
In a rare event, Angel Bunny was speaking the truth. Were Ponies truly better than man? Were they guilty of the same things they accused Man of?
Was man but the dark reflection of Equestria's future?
Angel looked ready to continue playing his devil's advocate role, before he sniffed the air.
The rabbit promptly bolted back onto his owner, in terror.
His owner matched his actions, before smelling something.....horrible.
A horrible smell, yet a natural smell at that. It was that noticeably different between a Skunk, and a human factory, and it made the Pegasus rather terrified.
What kind of animal.....could smell this badly?
As the leaves rustled around her, the Pegasus turned around to spy something dark emerge from the trees.
It was a tall creature, standing above any human she had seen. In fact, it stood taller than even her largest bear friends.
The hair was long and brown, with massive arms and chests. It also had quite large, rather less haired feet.
It stood like a man, and it's face looked like one to some extent, but even if she had not been inside the barrier she'd know that this was no man.
"Oh.....I've never seen a creature like you before" she greeted it, surprised but none the less willing to make friends with the bad smelling creature. Perhaps a bath would help that out "My name is Fluttershy, and I'm from Equestria. We're currently making all the nasty humans go away. This is Angel Bunny"
She gestured to the rabbit on her back, who looked into the beast's eyes.
The resulting glare that followed made Angel bolt into the forest.
"Wait, Angel!" Fluttershy this time actually shouted "That isn't very nice, you shouldn't run away from our new friend...."
As she yelled this, however, she failed to notice the sound of rustling leaves behind the creature. Or how it was glaring at her.
And definitely not how it was rising it's arms as if it planned to smash her with it's bipedal hands clenched together for a massive smashing blow.
......
One of the arguments used against the existence of Sasquatch, along with lack of dead bodies and lack of sightings, is the fact that many question if North America could even support such a creature with just plants.
The people who looked into Sasquatch had theories to explain this, though. One such argument was that the Sasquatch was an omnivore like several other primates, capable of eating meat. It was believed they ate deer, killing them by smashing them between the shoulders.
Horses had similar structures, and were likely just as fatal.
.....
The city of New Canterlot was built on top of what had once been San Francisco. Considering it was the home of a warring horse people and mentally altered Newfoals, it was a surprisingly nice looking city surrounding by forests.
Equestria prided on how open they were to the birds and critters from the woods to randomly greet them in their utopic city. They were far more inclusive than humans after all.
However, not all was well in New Canterlot.
"......I don't know how the humans are doing it, but they seem to be killing our outposts" Twilight Sparkle, personal student of the Princess, expressed her disbelief at a outdoor cafe as this worlds oddly self-propelled sun set behind her"I swear, humanity defies all logic".
"Impossible. Those brutes would be trying to invade our perfectly proper new homes if they could get in here" Rarity, friend and fashion designer, pointed out with a huff "It's probably just mountain slides".
".....Maybe...." Twilight mused to herself uneasily "Though it still doesn't explain why Fluttershy hasn't came back yet: it's been a month and we haven't heard anything from her".
"Twi', we're in a new world filled with creatures that Equestria never had. Sea Otters, Marmots, and all kinds of awesome Tortoises." Rainbow Dash, blue Pegasus and arguable best friend of Fluttershy, explained as if for a hundredth time. "Fluttershy gets really, really absorbed into that sort of thing. I mean, imagine what'll happen when the barrier saved the Amazon Rainforest, we'll never see her after that!"
Rarity was going to suggest they go look for their missing friend, when a Celestia-awful smell suddenly wafted towards them "Oh sweet Celestia! What horrible concoction did Pinkie Pie make this time!?"
However, not even the Pinkiest of Equestrians could have created a smell like that, forming all over the edge of New Canterlot. She could not have arranged the thousands of dark, shadowy figures to move through the surrounding forests.
She certainly could not have arranged for the terrifying bellowing.
All three Equestrian's eyes went wide in horror, as the bellowing began. From the forests edge, a howl had burst forth, sounding like it belonged to the horrors of Tartarus.
Then she saw them........
Charging out of the forest came giant, hairy men. All of them as large as some adolescent dragons, all of them moving with more muscle than Big Macintosh.
Some of them were armed with massive tree branches, as if crude clubs. Others with fists that looked like they could break houses.
And they looked......very angry. At them.
....
They say that nature can sense when something is wrong.
When a Tsunami looms, animals sense it and flee from the coasts.
A dog can sense disease in a human.
Man had observed that nature itself found the barrier engulfing the world to be terrifying. Animals actively ran from it, and avoiding the affected areas had disrupted migration routes across land, air, and sea. Many environmentalists feared the death of the Humpback Whale, the Monarch Butterfly, and the American Robin, among others, due to this disruption.
However......then the barrier shattered unexpectedly at no seeming provocation, rendering much of this fear mute.
.......
Half an hour after the barrier had fallen, military aircraft from offsea air-carrier had flown to the former San Francisco, wanting to discover what had befallen their enemy.
As the VTOL aircraft landed in the decimated streets, the soldiers inside were ready for anything. A vicious plague, a pro-human revolution, perhaps even trickery the likes of the original Conversion Bureaus.
However, as the doors opened, they found themselves greeted by dozens of dead Equestrians, surrounded by one dead creature. A creature many of these men had dismissed as only urban legend.
"Is that.....Bigfoot?" one commanding officer questioned in shock. He idly noted a media helicopter nearby, taking pictures.
"No Sergeant" one of the commanders of the first commanding officer replied, looking into the devasted city filled with many dead Ponies. He could see the dead bodies of two more great hairy apes, and the tracks of many, many more. He saw hair snagged in the ruined rubble, strange patches of blood everywhere, and a lingering foul odor "That, is a Bigfoot. It appears that they do in fact exist, and they appear to have saved the world".
This Commander would later be memorialized for his line, as well as his later one about hoping that there would never be a Sasquatch Bureau.
.....
Angel Bunny was the only survivor of Equestria. He later found a lady rabbit who could tolerate him, and a new species of rabbit emerged in the Rocky Mountains.
They were known for their foul natures.