Some standard lore before the awakening of the time walkers

In fifth era:

Ulfric Stormcloak's rebellion succeeded in kicking the empire out of Skyrim. Ulfric died before he could realize his dreams of reforming Skyrim, though. The next high king was incompetent.

The Dawmguard nearly succeeded in wiping out the Volkihar clan, but the new leader of the clan retaliated and the dawnguard were destroyed. This new leader was without doubt, the Dragonborn. However, the Dragonborn left Skyrim with his vampire clan after destroying the Dawnguard.

Skyrim fell to the Thalmor in the second great war. The high elven empire now controlled Cyrodiil, Valenwood, Eleswyr, the Summerset Isles and Skyrim. Hammerfell, High rock and Orsinum banded together to combat agressive Altmeri expansion as the second daggerfall covenant.

In the sixth era:

A mysterious Breton scientist unlocked the secrets of the Dwemer while working in a secret laboratory. He learned how to mine aetherium and create equipment out of said material. A secret that even elves didn't find out.

Vaccination was discovered by a talented Altmer scientist. Black Marsh annexed by the third AD, who suffered massive losses, but Argonian turncoats and political instability lead to the triumph of the Thalmor.

First working gun prototypes made. Industrialisation with Dwemer technology and studies into Dwemeri sciences lead to many marvels, including the creation of proper Physics, Chemistry and Biology, as well as a specific science dedicated to studying magic. This happened in the Second Daggerfall covenant, allowing them to fight off the third AD easily.

The third great war. The AD utterly destroyed by the magically and technologically superior Daggerfall Covenant, lead by a Dragonborn sent by Akatosh (not the LDB)

In seventh era:

Technology spread over the whole of Tamriel as peace finally took over. Akatosh's chosen ruled as "emperor". Emperors are now elected and the states are a set of united republics, but not a singular empire.

Scientists begin to make many fundamental discoveries to unlocking the secrets of Mundus. Technological progression began to snowball.

Eighth era:

Society has now progressed greatly, using Aetherium as a unlimited power source. Life extension, designer babies, genetic manipulation, directed energy weapons, laser swords and quantum computing all exist, as the sciences combined with magic made for rapid improvements.

15th era:

Sixth AD leader Theriel unbinds Akatosh and ends the world as it is known. This was the event that lead to the creation of the time walkers, of which Theriel is one. Because of the non linearity of time at this stage, the time walkers existed before Akatosh unbound