Okay, as promised, a (relatively) brief timeline of relevant events.
So the current Golarion year by the calendar in main use is 4711, with the count being done off of when the god Aroden, the Last Azlanti, raised the Startstone that had smashed into it from the depths of the Inner Sea, created the island of Kortos and city of Absalom around it, and ascended to full godhood as year 0 (he was previously this badass immortal wizard sort of guy of many an epic doing. Sort of.. The Emperor of Man from 40k, if you want a rough and somewhat terrible analogy).
-5293: Earthfall. Aboleths being otherwise rocked by an Azlant they had helped uplift, back in the day, manage via group ritual to call down the Starstone to smash into the world, destroying Azlant and creating a variety of geological calamities that plunge Golarion into darkness from ashfall. Societies end, and the majority of the elves leave the planet for several thousand years (with two notable exceptions that are not super relevant to you, but make for an interesting story if someone ever wants to muck around with the elves of Golarion). The world languishes in suffering and misery for well onto a thousand years before even the glimmerings of civilization return.
-1281: Taldor is founded by the scions of Azlanti refugees and local to the area tribal humans. Yes, this means Taldor is old as balls. The society is around 6,000 years old. What this means for you the player is that you have almost /six thousand years/ to mess around in as far as the history of anything you want to play with. Want your royal house to have had a Grand Prince in it? In six thousand years, I’m sure there can have been the one.
-43: Soldiers of the Padishah Empire of Kelesh claim and start to develop further the lands that will be known as Qadira, previously full of various tribes and nomads. From this an eventual terrible rivalry will be born and periodic warfare spark.
37: Taldor comes into its own as a fully developed nation and imperial power as it sends forth the first of its Armies of Exploration, a series of efforts to spread across, map and civilize (or depending on your perspective, subjugate) a still at least mostly barbarous Avistan (the Army of Exploration that goes to the continent of Garund ends in total failure). There are 7 of these across the next 2000 or so years, and all but the sixth see some measure of success, resulting in Taldor raising up vassal nations and otherwise coming to dominate most of the continent, with some exceptions (the upper north remains beyond their grasp more or less).
2632: The elves come back from parts unknown via their great portals, and reclaim their homeland of Kyonin. It’s not super relevant really other than for noting that the elves were gone for quite some time.
3203: Tar-Baphon, a wizard of notable evil and power who was killed by Aroden during his Aroden: the Legendary Journeys era returns to life as a lich of even more terrible power, and in the following years unites the orcs of the clanholds of Belkzen, and along with hordes and hordes of undead and monsters proceeds to spread terror and destruction across Avistan. And this might sound like standard dark fantasy overlord stuff, but the awesome thing about Tar-Baphon? He ultimately could not give a single fuck about conquering the world, his fanatically loyal followers, the undead worshipping philosophy he founds, any of it. It is all a means to a single obsessively hateful end: calling out Aroden to come back to the world for a rematch (the full gods ultimately restrain themselves from direct action on the world, usually, and it was long past when such shenanigans were tolerated for Aroden). The man is basically trying to burn the world to form the letters up to the heavens in continent scale fire and misery “come at me bro” or “Aroden, come out and play-ay” if you prefer. There’s something just almost ridiculously metal about that.
Anyway, this is relevant to note, because..
3754: Taldor launches the Shining Crusade against Tar-Baphon, the Whispering Tyrant. Taldor essentially is the vanguard of leading everyone and their mother that they can gather or rally in an effort to put down Tar-Baphon before he can ruin the world. It’s Taldor’s shining hour and finest moment, their big justification for having come into being (and something they obviously don’t shut up about at all in their fallen era, if given the excuse to brag). The fight against Tar-Baphon and reclaiming the lands under his dominion grinds on for 74 years of horrors, with even demigods falling to the lich. Eventually, where demigods and their ilk fail, it is a Taldan General, Arnisant, who gives his life to injure the lich so devastatingly, that they can imprison the Whispering Tyrant in his former citadel of Gallowspire, where he remains trapped to this day. Taldor founds the vassal state of Lastwall to stand watch over Gallowspire and the orcs of Belkzen. Arnisant has a big ol memorial in the city of Oppara. This is also something of Taldor’s last hurrah, as the decadence sets in not /that/ long after the end of the Shining Crusade.
4079: Qadira launches a massive invasion to conquer Taldor, coming across its southern border to begin some 500 odd years of brutal warfare (which I view as somewhat on and off and more on the scale of the way Rome and Parthia would brutalize each other across the years, but really, it’s fantasy, they had some 500 odd years of brutal back and forth warfare). Both sides afterwards will like to claim that they won, because reasons.
4082: Taking advantage of both Taldor’s increasing decadence and the distraction of the Qadiran invasion, the vassal nation of Cheliax declares independence, and over the next decade will move on to grab up a huge chunk of Taldor’s vassal states, becoming the dominant power of Avistan. (they’ll also grab even more territory in various places about 300 years later, but suffice to say, Cheliax becomes the new big empire of Avistan). Lastwall declares itself independent, noting that it can’t get involved one way or another, it needs to focus on its duty to contain Tar-Baphon and the orcs of Belkzen. No one from any side challenges this claim, because what are you going to do, take on the almost completely military nation who turn back endless orc hordes and various undead monsters as their day job? Good luck to you.
4528: Grand Prince Stavian I bans the worship of Sarenae in Taldor, largely to scapegoat something for Taldor’s tribulations. That it is the state faith of the nation trying to invade the hell out of them makes this pretty easy for people to accept, and Sarenae’s temples burn. The faith remains banned to this day.
4603: The period of hot war between Taldor and Qadira ends at last, settling into a mostly cold one. Both sides as noted claim victory because reasons. Neither really loses or gains any territory though.
4606: The date of Aroden’s prophesied return, when he will manifest in the world again to lead it to a golden age. Except that he doesn’t. He dies instead (how is unknown), breaking all prophecy in Golarion. Calamities galore ensue. Nations of the west coast of Garund drown from storms of impossible scale (storms wracking the Inner Sea region generally). Far to the north, the Worldwound opens, and the outpouring of demons necessitates the founding of Mendev by, well, the church of Iomedae really, and various anti demon crusades go down over the next decades that are a story for another time and not super relevant to you. A whole lot of bad shit goes down in this year, basically, and the most relevant to you is that Cheliax, who had been expecting to be the chosen land of Aroden to lead the world to glory, implodes on itself in a hell of multi sided civil war that goes back and forth for years.
4640: The chock full of diabolists house of Thrune seize control over Cheliax, ending the war. A great many of Cheliax’s vassal nations will decide “hey, I don’t feel like worshipping Asmodeus or being ruled by diabolists especially” and revolutions galore ensue over the coming years from Galt to Sargava. The only vassal states Cheliax manages to hold onto are Isger and Nidal, as far as it goes.
4667: The Red Revolution begins in Galt. Picture the French Revolution, but far bloodier, and where the dial gets stuck on Reign of Terror permanently. Galt doesn’t so much become an independent nation as a chaotic hell of governments that hang on for so long over a bloodthirsty mob before getting killed off and replaced.
4669: The People’s Revolution begins in Andoran with tiaras and rainbows and unicorns and Princess Celestia herself rolls in to tell us how Friendship is Magic (I really will stop sometime, I promise). Andoran becomes the independent nation of Andoran, home to freedom and light and Democracy Bear, the new leader of the Care bears (really, I will totally super stop, I mean it!).
8 months before campaign start: In the process of preventing her coup against the imperial throne, Grand Duke Maxentian Branas kills the Taldan Imperial Princess Eutropia. The ensuing political fallout and controversy results in his eventual exile, with some details of the coup itself seeming to be kept back from the general populace. This isn’t some canonical thing, this is my “removing an easy escape from a potential down the road succession crisis before game start” bit.
4711: Now. Grand Prince Stavian III has neither remarried to produce more children, nor yet named some heir. Though certainly still healthy, a tension has begun to rise from this. The Senate vigorously and ongoingly debates invasions of Qadira or Galt or doing in fact neither because who wants the mess of any of that. Game start.