The White Lords arrive in the Fallows from the Forbidden Lands. Their history claims that they are the children and slaves of mysterious beings known as the Titans. The White Lords use their magical powers to create a citadel shelter and enslave all of the small animals in the area.
Some of the White Lords take ordinary, unintelligent mice as mates, eventually producing intelligent children.
Sethias the Clever discovers how to instill intelligence in other rodents magically, creating the other intelligent races.
The White Lords go on the offensive against the predators in the area, leading their servants and slaves in a great war that eventually pacifies the Fallows.
Disagreements between the Lords about the future of their kingdom leads to its fragmentation. Individual Lords establish their own palaces in various locations around the Fallows.
Now separated, a few Lords are slain and eaten by predators, which then acquire dangerously high intelligence and some magical talent.
Several of these super-predators are banished from the kingdom by laying geases upon them to never come within sight of the Palace.
It becomes clear to some of the Lords that their lack of unity is dangerous to the kingdom in more ways than one. Civil war breaks out as the Lords fight to determine which of them will be Emperor.
Luciel the Magnificent is established as the First Emperor. His court consists of his surviving siblings and some of their "pureblooded" children (meaning that both of their parents were Lords).
The empire's borders are secured and several military outposts are created to guard against ground-based predators. The aerial cavalry is established to help mages get within spell-range of flying ones.
Sethias's experiments with the investment of intelligence are expanded to include inanimate objects. His attempts to create golems are a miserable failure, but his reanimation of the dead succeeds.
Horrified at the grisly results of Sethias's experiments, the Emperor orders him to cease, which he does.
The Emperor learns that Sethias has merely moved his experiments to his private estate, well away from the palace.
Fearing a new civil war if he moves against Sethias directly, the Emperor has Menara the Beautiful visit Sethias and poison him. Sethias's experiments are destroyed and his body placed in a hidden tomb.
In a trend that will continue for several generations, the aging Emperor Luciel the First expires quite suddenly. Menara seizes the throne, amidst a lot of grumbling about the Emperor's sudden demise.
The lack of formal rules of inheritance lead to a number of vicious power struggles whenever the current Emperor dies or seems likely to. Emperor Luciel the Third finally lays down formal rules which ensure that House Luciel will retain power indefinitely.
There is another civil war, in which three of House Luciel's enemies unite to overthrow the Emperor and replace him with a triumvarate. Despite briefly capturing the Imperial Palace, they are eventually defeated. All three houses are purged from the Imperial records, with all of their members being slain, enslaved, or exiled. It is believed that at least one rogue Lord escaped to lead a handful of survivors out of the kingdom to establish their own colony, but its location is never discovered.
An age of Peace and Prosperity ensues as all major predators have been slain or banished and the succession of the Imperial Throne passes peacefully from paw to paw for generations. A formal priesthood is established, which teaches the common folk to worship the original White Lords as gods and to honor the current rulers as their descendants.
The White Lords gradually become more decadent and complacent. Their magical powers wane to the point where a well trained normal mage can often out-perform them in practice. The army grows lax without a foe to fight and its numbers are allowed to dwindle. The priesthood becomes the de facto bureaucracy of the empire and grows rich on the taxes that they collect.
Now the Empire's military might is a mere vestige of what it once was. Clans of half-feral barbarian mice and rats seethe on the empire's borders, looking for signs of weakness. The White Lords spend most of their time conspiring against each other in power struggles, striving to win the favor of Emperor Luciel XXIV. The priests know that the magic that grants their race intelligence is running thin and believe that there is nothing that can be done to halt the process (nothing that they are willing to contemplate, at least).
Powerful merchants and minor nobles are the real law now, establishing private keeps and fortresses throughout the kingdom and ruling over the vicinity. Lawlessness and banditry is on the rise and shrews have been sighted inside the empire's borders again.
The Empire itself teeters on the edge of complete collapse but few realize how precarious the authority of the ruling classes really is. Her enemies see her weakness and conspire to replace the current rulers with themselves. Either some heroes will arise to restore the empire to greatness, or it will surely fall apart in mere generations. This is the age of the Hyperborean Mice.