Here’s what I know, if you see a mistake or want to add something please do. In places where I’m making assumptions or speculating, I try to be clear about it.
Fourth Era, Year 1. (4E 1) So Martin Septim, the last of the Septim bloodline dies while banishing Mehrunes Dagon, destroying the Amulet of Kings. This ends the Third Era and starts the Fourth Era.
Without an Emperor - With no Emperor to rule Tamriel, government falls to the Elder Council. Whenever the Elder Council becomes Regent to the throne, the Empire goes into a state of Martial Law under the councils direct control. This is supposed to last until the Council appoints a new Emperor. Lot of power here. The council is being led by High Chancellor Ocato, the same guy from the Mage Guild who was chilling in the Imperial Palace doing nothing during the events of TES:IV while the whole place was going to Oblivion.
The Empire Starts to Crumble - Sometime in the first 20 years of the Fourth Empire (Dates are speculation at this point) Black Marsh removes itself from the Empire. Since Black Marsh was never officially conquered or annexed into the Empire (It was added by way of a Provincial Treaty) it kinda makes sense that the Argonians would be the first ones to jump the sinking ship that is the Empire.
The Khajit neighors of Black Marsh in Elsweyr followed soon after. It can probably be assumed that the Mer retook the strip of land along their Eastern border, land lost to Cyrodil during the first Era, including the town of Leyawin. But this is just my conjecture, no solid info that I’ve seen.
The New Emperor - Sometime between 4E 1 and 4E 18, Titus Mede is crownded the New Emperor ( He is in power already in the book (The Infernal City) which happens around the 4E 40s. A former Colovian Warlord, he reportedly overtook the Imperial City by force with only 1000 men. By overthrowing the Regency of the Elder Council, he became the first Emperor to take the crown by force since the 2nd Era. (Correct me if I make mistakes here fellow Lore Scholars)
The Red Mountain Erupts – The Ministry of Truth ( The huge tunneled max security prison made in the floating rock above Canton that was stopped by Lord Vivic, seen in TES III: Morrowind) falls from the sky and crashes into Vvardenfell. This causes the volcano to erupt and most of the island is destroyed. What isn’t ruined is covered in ash and lava, and most of the vegetation and wildlife die off. This event is known as The Red Year.
Black Marsh invades Morrowind – The Argonians invade the mainland of Morrowind, crushing the reeling Dunmer who are still trying to recover from Vvardenfells lose. The fleeing Dunmer retreat to Sulstheim ( Sulstheim is the island from the TESIII:Bloodmoon expansion.)
Thalmor reclaimed Valenwood and the Summerset Isle. I’m having trouble finding information on Thalmor, but I know is has something to do with the Aldmeri Dominion (the birthplace of the elves)
The Birth of a Prince – Titus Mede fathers Attrebus Mede in 4E 18.
4E 40 – The Infernal City. The huge floating island with it’s city (Umbriel) is seen over Black Marsh, traveling towards Morrowind. It destroys the city of Lilmoth, which was recently reclaimed into Black Marsh following the secession from Empire.
There’s a huge gape here (150 years worth!!!) is missing. If anyone has any information please help me fill it in. I’m hoping a lot of this information will be revealed in the Skyrim books in Game. It’s safe to assume that much of the missing years is filled with war as Titus attempts to reestablish Tamriels Borders and reclaim lost territory from the Aldmeri Thalmos.
I’ve found little information on High Rock, Hammerfell or Orsinium. What I say here is mearly speculation on my part and if anyone has any solid info it would be much appreciated.
Hammerfell became part of the Empire during the Third Era after calling for help from Tiber Septim. Now that the Septim line has been broken, the Redguards may have split off like the Argonians and Khajit did. Imperial rule is not uniformly liked in Hammerfell, and it’s desert people were banished from the cities for their outspoken dislike of the Empire during the Third Era.
Orsinium was waiting for Imperial Review in order to become a True Province of the Empire before the fall of the Third Era. Whether the Province to be was acknowledged or not by Titus Mede will probably have a huge impact on where the Orc fall.
4E 200. Elder Scrolls V- The King of Skyrim dies, sparking a civil war among the Nords.