[All text below is pasted directly from PoorYorickDA's dA account. Links to the actual journals here and here (part II) if you are interested!]

INTRODUCTION
This war has seen it's fair share of atrocities committed against the ponykind, and perhaps none is more well known than the infamous practice of cutting off unicorn horns employed by House Earthborn. But it wasn't always like that. Here, we will look at the history of this terrifying practice, and how it came to be.

THE BEGINNINGS
The very first mention of cutting the horns of the fallen opponents can be dated back to March of the 7th year ATD (After The Disappearance), around the time of the first meetings of then newly formed alliance between House Earthborn and Thunderhoof buffalo tribe. Old warriors of the tribe would tell stories of their battles and their practices of taking the horns of their fallen enemies as a battle trophy. At that time, both Supreme Commander Applejack, and the Earth Council would consider such acts to be barbaric. Little did they know they soon too would give in to their own savagery.

FIRST BATTLE FOR NEW PONYVILLE (June 10th to June 11th, 8th year ATD)
New Ponyville - a small little town, built by unaligned settlers looking for a place to relive the old, peaceful days from before the war broke out. Being situated in the middle of Equestria, where many trade routes intersect, this small town would soon turn prosperous and rich. Of course, the major Houses couldn't just leave the strategically important town alone. Soon, House Earthborn and House Moon and Star would clash in a battle for control of New Ponyville. 35 000 Earthborn troops led by General Tree Branch battled the army of 22 000 Moon and Star soldiers, commanded by Battlemage Comet Trail. It was a sound victory for House Earthborn, that established the House's rule over the town. But soon, the importance of the victory itself would have to take a backseat to the discovery that was about to be made.

At that time, the fact that House Moon and Star has been practicing slavery on earth ponies and pegasi was considered nothing but a rumor. But now, all the evidence one pony could want has been laid upon the terrified eyes of the witnesses of the battle. Both pegasi and earth pony slave warriors captured by Earthborn troops wore multiple marks of heavy magical abuse, and worst of all - every single one of them had their cutie mark ripped off and replaced with a mockery of a cutie mark with a symbol of hoof shackles. The sounds of anger and disgust quickly filled the air around the town. General Tree Branch was quick to send for the Supreme Commander herself. When Applejack arrived at the town and witnessed the atrocities commited by Moon and Star, something in her mind snapped. It was at that moment when she suddently remembered the stories the buffalo warriors had told her long ago.

She was quick to order her troops to gather all of the captured unicorns from Moon and Star and bring them to their knees. She approached the captured Battlemage, and with a swift move of her blade, she dehorned and then immediately beheaded him. After a brief moment of silence, she gave a commanding look to General Tree Branch. He knew what had to be done - every single captured Moon and Star unicorn was to be dehorned and finally beheaded. Applejack silently, and with a grim look on her face, watched the entire execution to make sure none of her soldiers would go soft on these bastards.

APPLEJACK'S RETURN TO APPLELOOSA, THE APPLELOOSAN DECREE (June 20th, 8th year ATD)
After her return to the capital of the house, Supreme Commander Applejack immediately went to inform the Earth Council about the outcome of the battle and the grim discovery that has been made. The ponies gathered in the Halls of Stone were quick to begin their debate on the subject, but their political rambling was cut short by the head of the council - the matron of the Apple Clan herself - Granny Smith. The sudden silence that filled the Halls of Stone was a sign for Applejack to continue. She told the Council about everything -the battle, the captured slaves and the execution of the unicorns of Moon and Star.

Hours have passed when finally, the gates to the Halls of Stone have been opened, and a lanky figure of the Councils' spokespony accompanied by both Elder Matron Granny Smith and Supreme Commander Applejack emerged from the depths of the Halls to announce the new decree:

-Any unicorn caught in the territory of House Earthborn is to be immediately dehorned.
-Parents having a unicorn child are obliged to either perform an act of dehorning on their child themselves, or ask the local medical facility to perform the aforementioned act.
-Hiding a horned unicorn, or preventing/interrupting an act of dehorning are both acts of treason and therefore punishable by death.
-Any unicorn found fighting for, sympathising with - or otherwise being affiliated with House Moon and Star is to be immediately dehorned and executed.

THE AFTERMATH OF THE DECREE
After the decree has been announced, ponies gathered on the Appleloosa's town square began to whisper, argue, shout and finally fight each other over the decree. There were those who supported it wholeheartedly, and couldn't wait to make every unicorn suffer dehornification. Then, there were those who were against the decree, mostly earth ponies and pegasi who had unicorns as their friends or mates. Lastly, among the raging crowd, there stood a number of unicorns, shocked and paralyzed by what was happening around them. Soon, a riot broke out on the square, just in front of the Supreme Commander and the Elder Matron. Applejack was quick to order her honor guard to aid the town militia in quelling the riot, but she knew she needed to do something to calm the crowd, lest it will tear the town apart. She took her ceremonial, ornate hammer, and slammed it against the stone stairs which lead to the Halls of Stone. The resulting thundering sound made the crowd stop the infighting and turn their attention to their leader.

Applejack stood there for a moment, not moving, just measuring the gathered crowd with her one eye. Her stern look, one which only a loving, but harsh mother could give, made all of the ponies on the square freeze with fear. Finally, after putting her hammer down, she spoke to the crowd:

-"The Appleloosan Decree will officially come to life in fifteen days from now on. Untill then, any unicorn living under the banner of House Earthborn is free to leave with their horn intact. Unicorn refugee groups shall be granted escort services from local militia forces. Any unicorn wishing to serve House Earthborn will be allowed to, provided they first undergo dehornification."

-"M-my lady, if I may..." - the lanky and frail council spokespony standing next to AJ began to adress the supreme commander - "...the decree was supposed to have an immediate effect and I -um, I do not believe there is anything about letting unicorns go, and..."
-"Then add it" - Applejack responded with a calm voice, her eye still measuring the now tamed crowd.
-"B-but the Earth Council has to approve it first, and I don't believe..."
-"I said ADD IT!"
-"Y-yes, of course my lady!" - the spokespony bowed in fear - "By your command it shall be done."
-"Good." - Applejack responded, giving the pony a stern look - "once you're done, gather the messengers."
-"And what about you, my lady?"
-"There is a certain Elder Matron I need to talk to" - said AJ, turning her attention to Granny Smith.

Hmm, interesting...It's a strategic drain and targets a third of the population, though how it can effectively be policed in a era of porous borders is going to be interesting.

800423

Fun fact, unicorns actually account for slightly over one-fourth of the population of Equestria.

Some folks took the time to do a full Equestria Census. The full results are linked, but for short, I'll just post the images here...

Population broken down by species/type/race (call it whatever):

Population broken down by gender (note that fillies and colts are separate statistic for visual purposes):

I use these refs a lot, myself. They are taken directly from the show, so we're looking at canon stats, here. Not just guess-timates from fans looking for a quick plot point in their fic.

SO YES. House Earthborn is still effectively cutting off a major chunk of the population. Politically? This stands to be disastrous. Earth ponies are the majority in the population, but not over-overwhelmingly so. A surefire way to make a lot of enemies is to start chopping parts off of other people/ponies because of their race. But on the other hand, if you have a massive following such as House Earthborn does, then extreme actions can sometimes prove to solidify loyalty (from fear or from altered perspectives). Not to mention the sheer number of Earthborn 'zealots' that a political move like this would create. Nothing is more powerful or more dangerous than whole-hearted conviction.

AJ isn't as brutal as we though... while this isn't good, it is still better than enforcing dehorning without a choice. Though I don't think it affects House Earthborn's current policy toward House Moon and Star's horned enslavers.
Which now brings my opinion on these factions, from less bad to worst, at:
1 - House Stormwing ; 2 - House Earthborn ex-aequo with House Everfree ; 3 - House Whitegold ; 4 - House Moon and Star ; 5 - Cult of Laughter.

800519

What about the porous borders and the inability to police large swaths of empty land? What is the sizes and distances involved?

Hmm, plus what are the recognized and properly marked borders of the factions? I mean two, the Cult of Laughter and House Everfree technically have no borders. The first case as they are a decentralized terrorist cult and the second because they are...well...I doubt they'd care about squiggly lines on a pit of paper or bother posting up anything besides totems.

"Any unicorn caught in Earthborn territory is to be immediately dehorned."

I was going to make a unicorn loyal to Whitegold!

801330

A unicorn loyal to Whitegold would be perfectly fine. Earthborn are the ones who aren't fond of the head-pokers.

802356

That I know, but what if she was traveling around to sing and inadvertently walked through Earthborn territory? Oh God!!

806947

Well in that case, bite the chew stick while we grab the hacksaw. This'll just take a second.

806947

There is a sudden dust up, and suddenly a dozen Buffalo Warriors appear and surround you...then you are captured and quickly dehorned before being deported(IE: being tossed into a raging river that takes you out of their lands and into someone else's.)

Not to be mean or anything, but that is what they are sort of going for. More likely, given the large swaths of empty space...you'd probably not notice and probably already be out of the area by the time you do notice.

Earthborn - dehorning unicorns, part III
So, otherwordly things want to invade Equestria through House Moon and Star's careless use of magic? ... why am I reminded of something else?
Nice way to expand the AU possibilities while still letting people choose the time and situation we want.

809315
It does seem to take a good amount of inspiration from the Warhammer worlds, which I am more than happy with.

On that subject though, there is fair evidence to suggest that they already have invaded... The disappearance of Celestia and Luna aside, the formation of the Cult of Laughter centers around Pinkie Pie, who was the guinea pig in Twilight's attempted Alicorn transformation, and the Cult is known for it's connection with the dead and breeding mental insanity wherever they go, in addition to having connections and portals to the Laughing Mare's realm... If the Earthborn are trying to stop an invasion from extra-dimensional monstrosities... they're a bit late.

825212
Not to the point where House M&S realize its mistake and all Equestria unites against the Cult and the astral beasts, yet.

825295

True. However Twilight Sparkle is crazy... Applejack is rage driven. Rainbow was tricked into betraying her own home and now dreams of ancient glory days, Rarity has also gone crazy, and Fluttershy has withdrawn from Equestria as completely as she can... That they'll do the right thing and unify against the greater evil seems somewhat unlikely at this point. At least not before it's way too late.

825334
What I meant wasn't that they WOULD unite and stuff, but that in the current situation of Equestria, 15 years after the war started, the Cult and astral beasts' spread is still not enough grave so that the ponies would put an end to their quarrels and fight them together. I'm sorry if I worded this wrongly.
After that, the magic of friendship prevailing, the memories coming back, the Elements reuniting Equestria and themselves, etc... are my personal headcanon for ED.

825348

Quite true, and the personal interpretations and different story versions of them are what are going to hopefully make this site a pleasure to participate in! It would take a lot of work to redeem the ponies now in my opinion, but it would be interesting to see how that worked out...

Anyways, thank you for conversing with me. I like to talk tactics and probable outcomes... Back to House Earthborn and their dehorning though, I think what I was originally going for was too ineffective, too late. All ponies in Equestria seem to have a degree of magical connection, the unicorns are just the ones who can focus it the best. If the Cult's already there, then the precautions that Applejack's taking aren't just horrendous, they're useless, in my opinion. That was what I was originally going for I doth think.

Well, I imagined that if the Cult and the astral inhabitants were to win, Equestria and the whole planet would be doomed, most - if not all - of the Bearers dead, and the ponylands the home of the Laughing Dead and other abominations, forerver partying, dancing, and cackling, ... Bad ending.
I like to talk about this too, it was a nice talk.