So I kind of working on my own interpratation of Equestrian history. It's based of both details from canon and some assumption of mine to expand it. And well, considering that it is also created as the lore to my own fanfic the pre-season 7 assumption overwrite details from season 7 and newer. Though i still try to make them someway fit into the history.
So for example in my assumption Celestia and Luna were born a a few thousands of year after Starwirl death (or at least before season 7 he seemed to be dead), se they never meet season 7 finale theoritically prove it wrong, but assumption about when Starswirl lives was made, so i stick to it. But on the other hand i still incorporate the story with Shadow Pony and Pillars of Equestria, but just as being older events, and having nothing to do with creating of the Elements of Harmony, which already exist.
And one more thing anything besides the show and films i consider semicanonical, what simply mean - it could be so, but also could be different, so treat it just as suggestion.
I also sometimes incorporate some ideas (or just the names) from fandom, like Snowdrop or Nyx of the Night being historical figures here.

And this way I created over 10000 years of equestrian history, from the legendary golden era, ended by Millenium War to modern Equestria, known from series. It's timeline goes more like this(years count from the end of Millenium War, but mostly just indicative, so nearly all are actually "about year X"):
-1000 and formerly - Golden Era, times of First Kingdom of Equestria, ruled by legenary king Rex Equus (male alicorn, and first known alicorn, though not fully historical confirmed). The whole planet was ruled by him, and all races cooperate in peace and Harmony...
-1000 shortly after death (natural - alicorns aren't immortal or ageless, just have a very long lifespan(3000~4000 years)) of Rex Equus and alicornization of his student Princes Crystallo Amare it all ended. Before her coronation as queen she dissapear under mysterious circumstances. Then all races start to blame each other and the Millenium War began...
-1000 - 0 - The Millenium War, the damages were enormous, whole races were even wiped out...
0 - 25 Thanks to young mare named Unitas and her friends the war finally ended. Though the Kingdom from before the War wasn't fully recreated, now as Second Kingdom of Equestria it was only ponies' kingdom. Unitas, who become alicorn (first fully historical confirmed) was it first ruler. It wasn't easy process, one of the main obstacles, which nearly prevent it to happened was Rebellion of Unicornian Nobility (Unicornia was one of the biggest Kingdom in times of Millenium War, and as in many other countries that time slavery was there somthing considered as "normal", but after befriending Unitas princess Gemstone di Auro decided to abolish slavery, some of nobilities, mainly those which have benefits from slaves and slave market join forces with one pegasi kingdom to overthrow Gemstone and her father) but eventually all fractions did sign peace treaty, which also included so called "Charter of Fundamental Rights", which is basic of all laws in Equestrian Kingdoms even in present times. It's simply codified natural law.
Then Unitas through many reforms (so called Wisdom Reforms) create a powerfull and prospering country.
But few decads after Millenium War ends there was another problem. "Bipartite Revolution". It was simply revolution agains the Charter of Fundamental Rights, but in two oposite direction. The fraction consisting mainly of descendant of slave traders, and person who get benefits from it demanded relegalization of slavery. The second on the other hand were this who opt for absolute freedom, meaning it as freedom from morality, and even freedom to hurting or killing other actually.
After long and bloody fights Unitas finally menaged to defend Equestrian morality and for really long time Charter of Fundamental Rights wasn't questioned or denied again.
During her reign (I don't know yet what time more exactly) the Premother (first known Queen of changelings) tried to conquer The Second Kingdom of Equestria, but was stopped by Unitas and sent to Tartarus.
3500 - Unitas died. Her death seem as perfect occasion to strike for two neghbour countries - one of Griffins and on of Hippigriffins, though thans to tactical genius of pegasi generals and highly usage of weather controlling skills (and also advanege which ponies have from using magic) the aggressors were defeated. This was called "Storm War".
But then, after Storm War, and without next alicorn the next war started. It was civil war - the pegasi, earth ponies and unicorns fight for this who should rule. And this war destroy Second Kingdom of Equestria.
And thus the time of three tribes started. Yeah, now i Finally come to times from the series.
3750 - 3800 Windigos incident. So simply events form Hearts Warming play - the play give simplified but generally correct version of them. This what play didn't depicted is the fact that Clover the Clever became an alicorn. The new country was named after two previous kingdom of Equestria, which were kind of symbol of unity, especially among ponies. It was now the Third Kingdom of Equestria, which exist to present times.
Shortly after that Star Swirl banish sirens from this world, found Pillars of Equestria, and fight with Shadow Pony.
Then griffins declare war against Equetria, but they lose it.
5800 - Alicornization of prince Aurus
7500 - death of prince Clover
8269-8289 - "Sexual War"
8404 - Tragedy of Maretropolis
8500 - Finding of the Crystal Heart, founding of the Crystall Empire and begin of the Crystall Horn dynasty.
9250 - Alicornization of Celestia and Luna, great pony-changeling war, which eventually almost wiped out the changelings, and their Queen Arachne was decapitated by prince Aurus for her crimes againts ponykind. (Actually all ponies thought all changelings were wiped out, they didn't realise that Arachne's daughter - Chrysalis hide with some changelings and started to secretely recreate the hive.)
9300 - death of prince Aurus
9350 - Luna get to know Snodrop
10500 - last of Snowdrop's iceflake is used.
Life of Nyx of the Night (not strictly specified yet)
10939 - Sombra take over the Crystall Empire, kill it's rulers and then is sealed in ice by princesses Celestia and Luna.
10950 - Discord reign
10959 - Celestia and Luna find Cadance - lost daughter of the royal couple from Crystall Empire and last living member of Crystal Horn dynasty - after her alicornization
10980 - Tirek tried to steal ponies magic
10989 - threat of next pony-griffins war, solve this time throught diplomacy
11000 - Luna became Nightmare Moon and is banished to the moon
11200 - founding of the Wonderbolts
11600 - Mobius Moonstone (black magician, stoped by Celestia) incident
11655-11660 - Griffins' Deluge, kingdom of Griffonstone almost conqured huge part of east Equestria, but finally is pulled back and Equestria defend its whole territory. (2-3 griffons king before their kingdom fall)
11920 - founding of Ponyville
12000 - Return of Princess Luna.

I also have some events which i'm not sure yet where to put...
Alchamical War - before it zebras widely share they alchemical knowledge, but the power it could give (only magic can superior it) make some kingdom desire more and more... eventually zebras together with Kingdom of Eqestria won the war, and all knowledge about alchemy was put in zebras hooves. Their kingdom - Zebranda - become very isolationistic since then. [most likely in times of common reing of princes Clover and Aurus]
Grogar and Catrine - I plan to icnlude this two villains from previous generation but I don't know yet exactly when and how. (Grogar actually was mentioned in the show, Catrina fits the universe since MLP the Movie)
And this whole thread with Daring do and ruins she deiscovers

Generally what for i wrote all this? Well, I seek some cources of inspiration and maybe some ideas and suggestion to this version of history. I eventually gona to make it into something like this, though I'll write it in Polish* (though I don't exclue posibility of translating it).
Also I wonder in what semicanonical sources I can find inspirations and world building details (such as: historical figures, artifacts and events, and also geographical data). (I alreday know about "Journal of the Two Sisters" and "Twilight Sparkle and Spell of the Crystal Heart" and series "Legends of Magic" but what more?)
(i think many of the other discussions here can be helpfull too actually... but some more strict assistance would be even greater.)

*I'm from Poland, and my English is far from perfect, therefore I mainly write in Polish. And sorry if I write something not fully correctly...

6394469
Ok

6394469

Also I wonder in what semicanonical sources I can find inspirations and world building details (such as: historical figures, artifacts and events, and also geographical data). (I alreday know about "Journal of the Two Sisters" and "Twilight Sparkle and Spell of the Crystal Heart" and series "Legends of Magic" but what more?)

I don't think there's much more available as far as canon goes. Although a Celestia episode is coming up in S8 which may tell us something of her past.

6395621
Really nothing more? Actually after reading Your answer i recall myself of other series - Fiendship is Magic... which seem to be usefull in that topic. Well I actually forgot to mention that also depisction of other races are things i seek.
But Celestia episode seem promising. Even though I actually beginning to be a little bit disapointed in new seasons, I mean from the 7th.
I mean... we don't get the real opener for season 7, the final don't have a song (again) and... well some episodes has very wasted potential. Or worse, some were like parody of MLP and values it represents (I mean the new changeling society, and a little bit this "School of Friendship"). Actually I'm started to think that as much as narration always was kinda childish - but that's fully undertandable, considering main target of the show - but now the worldbuilding from Hasbro seems to become childish too. The whole time it was just idealistic (what i absolutly love about this series and universe) but not actually childish.
Don't take me wrong - there still are some great episodes, but... well also some really not so good... but i hope this one will be one of this great episodes. And say something about Celestia's past.