Between the two great events, Ainz held a more subdued gathering, of his world's leading historians. Because what good is history if it becomes distorted, corrupt, and forgotten? He did not wish the stories of his empire to be thought of as colorful myths told to disinterested schoolchildren. So he took the reigns of teacher to describe each millennium, then to field polite questions about the details within.
Unlike the first emperor of Earth's China, Qin Shi Huang, a generally laudable leader in Ainz' estimation, who had wanted history to begin with his reign, so had all the history books burned and the historians buried alive, or so the story went, Ainz sought to preserve history.
He used to mention this event to the assembled historians while saying that he would never do such a thing (the tacit threat remained that if they annoyed him enough he might change his mind). But he discovered that their inclination was instead to "magnify and glorify" his name too much, which was also to be discouraged as it would tend to make their students more skeptical. So instead Ainz tried to be objective and to be more forthcoming in his answers, so that the truth would win out.
His first era was the time before his arrival and the time of troubles, which was not a complete millennium but close to it. Yet it was of intense interest to historians, because history had not yet been formulated as a formal study on the New World, mythology had not been separated from fact, evidence was plentiful, but concealed, and most of all, some who were alive then were still alive, but disinclined to talk about their pasts, except with each other.
More practically, it was also the beginning of documentary evidence in the form of the Nazarick Memory Bank, a brilliant idea on his part, Ainz thought, that had paid many dividends over the course of years. A historian with just one account is uncertain; but give him two vaguely similar accounts and both become fact.
It began in the most trivial of ways. In an idle moment, Ainz was reminiscing about a discussion he had in YGGDRASIL with Tabula Smaragdina, about a horror movie he had enjoyed, but try as he might, he could not remember its name. But this brought the realization that his memory was not unusually good, and over time he would forget details and his memories would become corrupt, unless he made it a point to record them. From there he realized the problem might also extend to the NPCs and individuals aligned with Nazarick. With much thought, this led to the creation of the Nazarick Memory Bank, or NMB.
In small rooms conducive to remembering were "console homonculi" that would record memories, written and oral. Once a given memory was complete, from several viewpoints, it would be transported to permanent storage in the Nazarick treasury under good security. Ainz very carefully explained to the guardians and other invited contributors the difference between objective and subjective reports, and how both were important, and the guiding, but not required, format for them to use to insure important details were recorded. It used the universal planning format first created by Sun Tzu, adapted and modified by military organizations ever since, with a few wise additions, but no deletions. An eternal masterpiece of organization and planning.
Then, as a final twist, Ainz whimsically added a strange condition. Before a guardian would publish a report, they would select one of the 64 hexagrams of the I Ching as its symbol, whichever one they thought most descriptive, most relevant to that report. With titles like "Hexagram for the Creative Heaven" and "Hexagram for Duration", it would help them overcome their natural rigidity of the mind.
Though he later discovered that, at least at first, they thought of this last idea as agonizing torture and filled with painful self-doubt, until they finally grasped that it was not factual, but purely based on their spur of the moment opinion. For a time it also led one or two of them to develop an interest in fortune telling as a hobby, but that, fortunately, didn't last.
For his own use, Ainz realized that he was far too much caught up in self-reflection, yet he had no peers or friends in which to confide. Even his closest, most beloved NPCs could not be fully trusted with what he knew, felt, or feared. For this reason he needed his own personal, secret, safe analyst; a confessor; a confidant; a sounding board; and, in the final analysis, a safe means to experiment with the whole truth, new ideas and innermost thoughts. A psychiatrist in a box. That Demiurge's scientists were, with considerable guidance, eventually able to make such a thing to his satisfaction finally gave Ainz a means to relieve much emotional stress. In return, it gave these scientists many new insights into artificial intelligence.
Such an analyst would be a very useful tool, but also a very dangerous weapon. Therefore it must be exclusive to Ainz, and kept isolated from anyone else. Paradoxically, it must be allowed great access to much information. It must also be uninhibited in what it tells Ainz. And finally, if part of it became corrupted or dangerous or no longer useful, that part must be able to be wiped and reset without harm to the whole.
The analyst would have to be immobile, and it would instantly self destruct if anyone other than Ainz were to enter its room or attempt to recover data from it.
Areas of the brain of the analyst would have to be subdivided into modes, so that even with the same data input, the output of each mode would be different. Part would be fawning sycophant; another part bitter enemy; another part indifferent, or neutral; another part cynical and skeptical; parts would be optimistic and pessimistic; part would be motivated by extreme greed and avarice; another part extremely calculating; another part filled with blind rage, hate and desire for revenge; another part that is deceptive and wishing to conceal the truth, and a large part filled with beneficence and compassion, to balance the rest.
Since he was denied strong emotions by the suppression field, he wanted them by proxy.
The first millennium of his empire was a time of great growth and creation. Ainz' original plan was that each millennium would somewhat follow the five traditional elements in character. Wood or Spring, Fire or Summer, Earth or late Summer, Metal or Autumn, and Water or Winter. Extrapolated from nature in a farming culture into society as a whole.
After growth and creation, Spring, would be a season of vitality, Summer, fruiting and order. Then a season of late Summer, Earth, a time of moderation. Then a millenium season of harvest and prosperity, leading into the decay and rot of Fall. And this would be followed by the fifth millenium season, of fallow and washing away the waste, Winter, so that the slate would be wiped clean and the process could begin anew. This was a tried and true method used by some in Asia, with successor leaders trained for their elemental role, which had proven itself over time. Water emperors, like the first emperor of China, tended to great destruction and bloodshed, as was expected of them by everyone else.
If they carried out their respective roles as leaders, their entire realm would support them. If they opposed their role, their court and realm would act incompetent and inefficient, and nothing would change. In their own ways, each of these seasons would be imbalanced, but these imbalances would be canceled in the entire system, which would as a whole be balanced. A greater order to things would prevail.
At least this was Ainz' idea of how his society should evolve over time. He did not ask himself how he knew this, as he had not learned this in school. But he knew that he somehow he knew many things he had never been taught.
However, this being said, near the end of a very constructive millenium, circumstances intervened in the form of a message from Demiurge, requesting an immediate visit by Ainz to the chief astronomical observatory in the New World, located in the Azerlisia Mountains. This revealed that a planetoid body had entered their solar system at high speed, and while it could not be predicted to menace the New World, it might create some disruption were it to pass nearby. In and of itself this was only interesting, until the planetoid changed course. As a potential threat, Ainz then directed Demiurge to immediately begin efforts to develop world items, or even the new class of planetary items, to protect the world from it if necessary. The capability of making uniquely New World items of immense power, far stronger than many YGGDRASIL items, had been a cornerstone of his empire.
This possible threat also represented the beginning of their space program. The cooperative venture of scientists, merchants, and casters soon resulted in grand leaps in technology, resulting in a fleet of very fast exploratory ships and very heavily armed warships and emergency evacuation ships. There was no expectation that they could destroy the planetoid from afar, only to get close enough to engage it with destructive items. Demiurge begged Ainz to let him be on the first exploratory ship, bringing magical means whereby he could destroy the planetoid if needed, even if he had to do so from within. When first it was seen, he reported that it was not round like a natural body, but shaped more like a cylindrical barrel, crafted to be an immense spaceship. It had a giant dock, more than able to accommodate the entire ship. Within there were no signs of life.
There was, however, a great corridor inscribed with thousands of different language iterations of the same simple phrase, later determined to be the name of the ship. "Research Master Archive." When Demiurge passed through the corridor and entered through a great door, he discovered what at least this part of the ship was. He found a gigantic research library able to, without any living beings aboard, study and record knowledge of seemingly endless planets on its quest through the galaxy. Something was wrong, however, as it had run out of storage capacity, so that as new worlds were recorded, the oldest of its data was lost. To rendezvous with this ship, even for a short time, was the highlight of Demiurge's life. A treasury of incalculable value. With his determination that it was not a tangible threat, the character of the mission changed completely.
The discovery of a portrait of what he suspected was one of the creators of the spaceship, a large, handsome demonic being with cloven hooves, leathery wings, horns, and a tail, convinced him of their overall beneficence, though he was quite abashed that they considered themselves "Overlords."
With its final adjustments to its course, it entered orbit around the New World. Working around the clock, Demiurge and every scientist and scholar with him were only able to record the smallest fraction of its data before the ship itself made it clear it was preparing to automatically leave. Even so, sorting through such a mountain of information for what was useful would take ages. Demiurge also noted with interest that within the ship were signs of other visitors and some battle damage, but no carnage. Cleaned but not repaired. And an artifact.
It appeared to be a battle axe, not a primitive weapon, but machined, and of extraordinary mass. With later examination in a laboratory, it proved to be an impossible thing. Made of artificial elements of extreme mass, normally so unstable that they would disintegrate in a tiny fraction of a second. Or rather, stable isotopes of those elements, alloyed together. Impossible for any number of reasons. He guessed that it had extra-universal origins, from a universe where such things could exist, yet had somehow retained their character in this one.
Demiurge then speculated that a type of magic had been used so that to its user it would feel lightweight, yet would impact the user's target like a bladed castle gate, cutting through most things with ease. He imagined that once casters could figure out how to restore its magic, it would make a fine gift for Ainz himself.
The greatest conclusions of this spaceship were that first, there existed very advanced civilizations who might become a threat in the future; second that even with their fleet of ships, which needed to be vastly greater in number, they needed a gate technology to cross the limitless void of space faster. And it would still take many durable and long lived pilots, likely automatons. The third conclusion was that once they had the means, they should pursue this archive, take control of it, and make it the property of Nazarick as a permanently orbiting body.
And fourth, why had its creators seemingly abandoned it?
Last, he noted from the ship's charted path, displayed on a great viewer in the library, that it had changed its course to widely avoid several stars, some of which had later exploded, while others had the potential to explode. And that a handful of such stars were close enough to the New World to destroy it, sooner or later. It gave him centuries of concern. How might they neutralize a star?
This second millenium changed the course of the Empire in ways that reminded Ainz of the original purpose of YGGDRASIL, one of exploration and discovery. So even before its start, he dedicated the third millenium to that purpose.