A pivotal plot-point in the upcoming story and part of my headcanon's history.

Little is told of the rise of Hycarion. Its fall, however, is recalled quite often.
When Rememberly came to the throne, ruling from the oldest and greatest city of Hycarion, her rule was...disputed.
While the common folk loved her to the point of deification, many of the local noble families saw her as a threat.
Her reforms came too swiftly and too often, proving costly to their households. Rememberly's insistence that this was their responsibility didn't help matters.
To this day, historians regard Rememberly as a good and loving individual but one who went into political matters without the necessary tact and understanding. Equestria, at the time, was not in a good way and, while she improved the lives of her subjects, it was only short-term. When the food was gone, swords would be drawn.
And swords were indeed drawn. Upon Rememberly and her chief supporters. Only a young Star-Swirl escaped with a barely alive Rememberly (Though it's said that Surprise, Rememberly's Jester and Spymaster, walks as a benevolent but vindictive lich plaguing the descendants of those who slew her)
Those who remained loyal to Rememberly departed for what would become the Flutter Valley where she would recover and rule wisely and justly in a land of peace and plenty...until the Barbarian Invasion led by the Warlord Tirek and his foul servants.
Those tales are many and vary from mouth to mouth. What is recorded in Canterlot's annals that relates to the return of the Alicorns in Equestria and their ascension to power goes thusly.

The noble families sought to restore Equestria to its old ways but soon fell out amongst themselves, too caught up infighting to pay all that much attention to what was taking place outside of their domain where the Three Tribes of Unicorn, Pegasi and Earth Pony grew in power and resources and slowly mended ties with each other.
Star-Swirl appeared to each of them as a travelling adviser, Rememberly nowhere to be seen.
To this day, nopony knows what happened to her.

The six founders met at a quiet village between their three domains to discuss terms of their triple alliance where they beheld the birth of Laurelore the Firsticorn, the Great Rejuvenator.
It is in this time that Star-Swirl returned to Hycarion to foretell doom and destruction upon those that betrayed their Princess and to warn them the time of reckoning was at hoof.
Sure enough, the Three Tribes united, the Firsticorn as their figurehead, and defeated Hycarion's armies time and time again. Star-Swirl's warnings had been heard and often spoken of among those that dwelt outside of the capital and many threw down their blades and defected.
As the Alliance neared their very gates, the leaders of Hycarion elected to hire a large mercenary army to keep order in their city. Far more skilled and keen in battle, they proved a match for the Alliance, driving them back substantially.
So the Alliance tried a different tactic.
(Each retelling of the events vary on who came up with this tactic. Unicorns profess it was Clover and Platinum, Pegasi are certain it was Pansy and Hurricane and earth ponies claim it was Smart Cookie and Puddinghead, while more recent, 'unbiased' sources believe it was more likely to be Star-Swirl or Laurelore herself. It is difficult to say for sure)
Faced with great loss of life and resources in pitched battle, the Tribes expanded their domain by assimilating every field, village and outpost, undefended by the mercenary army holding out at the capital, reducing Hycarion's revenue to barely a few dozen bits a year. Far too little to pay for the Mercenary Army who swiftly turned upon their masters and razed the city.

With the loss of Hycarion, the Alliance began the construction of Canterlot, overlooking the quiet little village where the Firsticorn was born.
However, the various noble families had not been entirely idle, simply opportunistic.
Less powerful households now saw fit to make their move, intending on attacking a weakened and occupied foe and seizing power for themselves at last.
The self-proclaimed kings and warlords set up their own petty states all over outer Equestria. Countless were their number and widely varied in strength and power. Some endured whole centuries of prolonged war, others rose and fell in days.
All of them, however, toppled eventually, their households conceding and granted amnesty, largely deprived of the power they'd once held.
Their former states and territories now go on to make up the majority of what is now known as 'The Outskirts' a place whose reputation puts most central Equestrians off visiting.
This suits the denizens of the outskirts for, even after countless millennia, the wounds of their defeat still burn in some of their hearts and a thankfully scarce few dream of the day they reclaim the powers that were once theirs to wield against all that had wronged them.

A interesting pivotal plot-point and head canon you have here.

5998355 5998357 Indeed.