There are snippets of context on the Empire's history covered in the notes, though it's not really meant as a history primer, and it's also prompting Leareth's memory. The system of compulsions doesn't date back to the founding of the Empire under the First Emperor; originally, compulsions were only used as an alternative to execution for serious crimes. The expansion to "everyone important" happened later, after the First Emperor and his top advisors, including Arvad - who was one of Leareth's lives - were messily murdered, as part of a plot by followers of Atet, one of the gods worshipped in the region near the tiny initial core of the Empire, and the Empire collapsed into civil war until the Second Emperor - the next of Leareth's incarnations - took power. And started considering options to make it at least harder for assassination plots to reach the core government of the Empire. ...And then, of course, the system became a self-reinforcing one, and in the periods between when he was alive and in a position of significant power, it had a definite tendency to start degrading into worse, more pointlessly exploitative versions of what Leareth had initially built.
Which...does feel predictable now, but Leareth genuinely isn't sure how predictable it was without the benefit of hindsight, or the deeper understanding of governments and politics that he's built gradually over centuries? And - certainly at the start, less than two hundred years after the Cataclysm, he must have been mostly caught up in desperation. People were starving, Changecreatures were at large even well outside the Pelagirs per se, bandits were roaming unchecked, and the survival of civilization must have felt so, so tenuous.
He must have chosen to come back a number of times when not strictly bound to it; his immediate previous incarnation, for example, was an immigrant born outside the Empire entirely, and it's not in these particular notes but it seems plausible on other occasions he came back in the body of a common-born youngster whose mage-gift had yet to be identified. It's still a minority of the Empire's population under compulsions, and a much smaller minority of twelve to fourteen year olds; it's just that to do anything interesting - and, for a long time, he thinks the Empire was the best place on the continent for that - you need to be near the centers of power, and being trusted with power is something the Empire runs entirely on mind control.
Altarrin does not seem to have been impaired in keeping his records updated, or even in sometimes Gating off to do personal errands outside the Empire entirely. He was bound by compulsions to obey direct orders from the Emperor, but it seems like most of the day-to-day work, once he was in a senior position, involved operating with quite a lot of autonomy; he couldn't do anything to sabotage the Empire, but he doubts he wanted to, and the compulsions allowed him to have personal goals that weren't about obeying orders. Also, it was one of the eras when "serve the Empire" was ranked above "serve the Emperor", and Leareth suspects that - given how he conceptualized the Empire as his own creation, and as a vision he had yet to achieve fully - he could eke quite a lot of flexibility out of that, and justify maintaining his records and resource base as obviously in the interests of the true spirit of the Empire.
- anyway, in broad strokes, Altarrin spent his career accumulating political favors and then using them to root out corruption and nudge the Empire's laws and institutions toward the more functional and human-welfare-improving state that he wanted. And, of course, holding off the inevitable external and internal threats to the Empire, many of which he diagnosed as directly god-related plots. (The northwestern-most province of the Empire was nudging up against Iftel, by then, and despite its relatively low population - it was cold and arid with poor farmland and a short growing season, and had been annexed mainly for mining - Isk was the ultimate source of a truly excessive amount of sabotage. The Empire's southern border also expanded on Altarrin's watch, annexing the country formerly known as Oris and, thus, involuntarily adding a population base who - understandably - had some strong resentment against the Empire.)
Mostly it seems like grinding, unrewarding work, and even the tersely summarized notes, written near the end of Altarrin's life, are permeated with a feeling of weariness. At least according to Leareth's sense of it now, Altarrin seems to have focused his attention on broadly reasonable things – maybe with the exception of his military work on expanding the Empire, which Leareth has at best very mixed feelings about, particularly Altarrin successfully crushing a particular thorny rebellion in newly-annexed Oris that happened at the same time as a couple of very poorly timed rebellions by Imperial generals in long-established provinces. But a personal history of glorious military victories was clearly one of the currencies of influence that Altarrin used to root out the inevitable abuses of power that had crept up since the last time he had enough sway to do anything about them.
Outside of his official duties, Altarrin invested quite a lot of time and attention in finding and mentoring particularly promising young people – especially people who genuinely cared about and believed in the ideals of the Empire, but who lacked the political savviness to survive in the Imperial court. There are dozens of names mentioned, often with real fondness leaking through.
(Leareth doesn't remember any of them)
Altarrin's largest success, at least according to his own summary, was in cultivating, successfully appointing, and mentoring his chosen candidate for Emperor, Bastran IV. Someone who, against the odds, genuinely and deeply cared about doing right by the people of the Empire. ...And was still constrained, by the Empire's laws and culture and the other power bases he needed to placate, by the weight and momentum of six hundred years of history, but he does, in fact, seem to have worked with selfless dedication toward the welfare of his citizens for his entire life.
(Bastran, too, would have been under compulsions since childhood. As Emperor, he was under only a single and quite flexible compulsion, to loyally serve the good of the Empire.)
(There's a short addendum to the notes, presumably added later, because it states that Altarrin died at the hand of rebels on the western border - followers of Anathei, this time, though internal politics of the Empire played a part in why he was there - several decades after the pacification of the rebellion in Oris. There was nothing particularly unique or brilliant about the plot, Altarrin had survived dozens if not hundreds of attempts on his life, but he had rolled the dice over and over for his entire life, and eventually he wasn't careful enough.
A handful of years later, Bastran IV was found dead by poison in his own quarters. The assassin, if there was one, was never identified. The addendum to the notes states, without any further explanation, that Altarrin wouldn't be shocked if his death had been a suicide, though he would have expected the compulsion of service to at least make suicide difficult to consider.)