The Conversion Bureau never made any sense anyway, but here are some places where it would have made less sense.
Not necessarily worlds where the ponies would lose the fight - just worlds where conversion wouldn't logically work.

Before suggesting a World, read the index to make sure I haven't done it already.

On July 17th, 2023, satellites around the world began to pick up a strange radiation source coming from the North Pacific, just above Hawaii. Just as the US, Japan, Australia and other such nations along the Pacific begin to investigate, something covers the entire North Pacific in blinding light, a loud crack rippling through the air. When the light finally died down and humanity rubbed it's eyes in shock, they saw none other than Equestria.

The first contact had gone well enough, with pony and human delegations meeting in New York, Celestia herself showing up for a moment. They claimed that the appearance of Equestria was purely accidental, a 'magical mishap' as they put it. They established 'Conversion Bureaus' around the globe, establishments for the sole purpose of permanently changing a human into a pony.

As it turned out, this was all a ruse. Shortly after the final conversion bureau was built, Celestia herself declared humanity to be a 'vile' and 'unfit' species, citing examples such as their wars, their pollution, and so on. All at once, the Conversion Centers released hordes of Pegasi and Unicorns, bent on forcibly turning all of humanity into 'peace-loving' ponies.

All at once, millions of humans were transformed. Military bases sabotaged. The world couldn't even get a missile out of the ground in time, much less perform a coordinated counter-assault. Humanity simply wasn't prepared for this.

But as it turned out, there were other players in the game. Humanity had gotten out of fixes much worse than this before, and they didn't even realize it. Organizations, unknown to even the world elite, sat beneath the surface of the Earth or disguised as ordinary facilities, prepared to do everything in their power to prevent the extinction of humanity.

As humanity panics, the SCP Foundation takes action.

THIS STORY IS A CROSSOVER WITH MY LITTLE PONY: FRIENDSHIP IS MAGIC AND THE SCP FOUNDATION.

THE SCP FOUNDATION MYTHOS IS A COLLABORATIVE WRITING SITE CONTAINING THOUSANDS OF USER-SUBMITTED ARTICLES DESCRIBING FICTIONAL, ANOMALOUS OBJECTS AND ENTITIES.

I DO NOT OWN MY LITTLE PONY: FRIENDSHIP IS MAGIC, NOR DO I OWN THE SCP FOUNDATION. ALL RIGHTS RESERVED.

This story is undergoing a massive rewrite. Expect everything to change soon.

A Russian MVD Spetsnaz team is sent smashing into the ground after the Mil Mi-24 they were in was knocked out of the air. A short time later, the crew and passengers wake up to find themselves in the wreck of the helicopter - but nowhere near Moscow.

As they desperately attempt to find out where they are, they will discover that they are not alone: Other humans have also found themselves in similar situations. However, these disorganized forces may soon be fighting for their survival, against an enemy that they could never have planned for...

The original version of the story, as published 2013-2015, can be found here for those that want to read it as it was. Editing on the original story was done by The Rainbow Brony, and I am thankful for the time that he put into the story to make it better than it would have been otherwise.

It has been nearly sixty years since humanity witnessed the devastation of a World War, or any other kind of large-scale conflict. Equestria's abstinence has been even longer, with battles that rage across the entire land not being seen for centuries. Though both have seen their share of small-scale skirmishes, a duel of total annihilation across a large scale has been avoided by both sides time and again.

But peace is never lasting. For both sides, it lies on a cliff, requiring only one good push to send the participants into a plunge of death. Equestria's unexpected appearance may turn into that final push, as alliances, deception, and distrust threaten to launch a conflict that will lead both worlds to utter ruin.

CREDITS:
This work contains characters and parts created and written by other authors. I am grateful to have become friends with each of them.
Captain Jack R. Williams of the U.S.S. Boxer (LHD-4) created and written by An A10 Warthog
Captain Wilbur Hart and the U.S.S. Tippecanoe (CG-74) created and written by Totallynotabrony
Captain Starry Skies and the R.E.S. Horseshoe Bay (CSG-2) created and written by The Grey Pegasus
H.M.A.S. Sydney created and written by An Iowa Class Battleship
H.M.C.S. Presence created by Sockeye101 and written by The Rainbow Brony
USAF Pararescue team Prancer Two created and written by CptBrony
Carter Jones of the 130th Engineer Brigade written by Routine Blast
1st LT. Silverglow and the Karalian Army created and written by Silverstein.
Sergeant Jeff Thompson of C Troop, Royal Canadian Dragoons created and written by Goldenarbiter
Junior Sergeant Korrector and the 115th Motor-Rifle Division created and written by Kalash93
(More may be added over time)

NOTES:
Rated T for violence and language.
My Little Pony: Friendship is Magic created by Lauren Faust and owned by Hasbro.
Any and all other works belong to their respective creators.

(STORY IS UNDERGOING REEDITING)
“Demonstrate to the world, there is ‘No Better Friend, No Worse Enemy’ than a U.S. Marine.”
~Gen. James Mattis

Excited for his first deployment, young marine LCpl. Kevin Brooke and his fellow squad mates of Bravo Company 2nd Battalion 1st Marines, begin their journey through the Pacific Ocean with the U.S. Navy carrier fleet. On their second day of voyage, they encounter a large floating crystal, ending in a swift and devastating battle.

After awakening in an unknown world, four ships (‘USS’ Anchorage, Princeton, Spruance & Michael Murphy) must adapt to a land filled with talking ponies while finding their way back home. However, during their stay, Queen Chrysalis rebuilds her army to take on her new enemies, and Brooke slowly unfolds the depths of a forgotten past.

NOTICE:
*Edited/Proofread by Dumbgamer999, totallynotabrony, & Groggari
*Rated for graphic violence, language, and gore
*Additional Tags: Random (occurs a few times in the story), Comedy, Dark, Thriller
*All characters (humans) in this story are fictional and are not affiliated with the U.S. military and other international militaries
*This story takes place several months after S03E02
*My Little Pony: Friendship is Magic is owned by Hasbro Studios & Lauren Faust

Featured:
-November 24, 2014 -- Wow... I have no words what to say about this. Thanks so much for this achievement.

This story is a sequel to A Glimmer of Hope in the Black

Declaration from White Clover
Date(s): April 26th
Relevant Case: Ponyville Mass Disappearance (#3467)
Classification: Top Secret

To whom it may concern,

As of this declaration, all those stationed in the town of Ponyville tasked with investigating the citizenship’s disappearance are to begin immediate psychological evaluations. If the results of an individual’s evaluation is considered troubling, a mandatory period of rest and recovery will be required before they may resume duty on any case.

Special thanks to Petrichord, Solocitizen, Garnot, Floydien, and Door Belle for their help with the writing, editing or proofreading of this story.

A print version of all the stories in this series can be found here.

I really don't know where this came from.

What if the teleportation was messed up. What if Equistria missed our earth but hit a different one. One scarred by nuclear fire and humans already fighting for their right to exist. Against machines. Skynet and humans must decide. Die by the ponies or band together and fight back.