Getting Started

I actually bought Stellaris in the fall of 2016, but never got around to trying it - being both busy with other projects and somewhat intimidated by its scale - until two years later, on a whim after growing bored with a Factorio playthrough that was proving extremely grindy. Unlike with most games, my experience with Stellaris did not follow a progression of several weeks or months of vanilla, followed by several months of playing mods, before I tried making any of my own; I used mods from the very beginning, and went less than a week before delving into their creation. For my very first playthrough, I downloaded one of many "Dragon Species" mods on the workshop, and created an empire that sounded like the good guys, with xenophile, materialist, and egalitarian ethics, but otherwise templated after the basic Earth start. I then tried a small first campaign, with one AI empire and one fallen empire.

Quite rapidly I realized that the egalitarian ethic forced government modes that were extremely inconvenient - regular elections were constantly forcing out my good rulers and constantly appropriating random scientists I was using for critical surveying or research. As a result, I wrote a small custom-edict mod that shifted the ethics of the empire to replace egalitarian with authoritarian, and shift towards a centralized authority type.

Founding the Commonwealth

That save did not last very long - 200 stars went by in a week - but by the end I had greatly expanded upon the species mod, and ended up splitting it into a totally new species mod, and started work on a custom prescripted country, the Aleran Commonwealth. The core concept of this empire design was as a foil to the genocidal empires, which come with significant gameplay advantages (enough so that at the time the meme of "I spawned near one, time for a new save" was widespread). Not only did I want to have a strong gameplay position - without being forced to play as "the bad guys", which I never want to do in any game - but I felt that their existence with unopposed advantages made for a very lopsided galaxy.

I started off by creating a custom authority model that was more clearly well-intentioned than "dictatorial", as well as matching civics.

Next were a lot of backstory, a custom starter system and surrounding systems, and then onto the custom casus belli and war goal system.

.
From there, I started a new save in a much larger and more densely populated galaxy. Over the course of this playthrough, I developed further systems to both augment the intended playstyle and guide the player into it, including the gradual expansion boosts, the custom buildings, and the supervisory faction. I also developed late-game content, including the custom colossus weapons.

By the end of the playthrough, I had a country with enough flavor, content, and custom gameplay that it was releaseable as a proper mod, and I published it on the workshop.

Unfortunately, the 2.2 "Le Guin" update came out a couple weeks later, making the mod partly incompatible and requiring significant updating work, at a time when I had already moved on from Stellaris to other projects.

Deeper Story

Fast-forward to the summer of 2019, where I revisited Stellaris, and with it the Commonwealth. Rather than update it - since further game updates were seemingly imminent - I decided to delve deeper into the story and theming; I added more flavor content, more guidance into the proper play style, more buffs for specific situations - notably against the Great Khan, who now was treated like the threat he was. I also added a lot more events, especially when the Commonwealth was an AI player against a human empire they would target, where it would be a more threatening opponent, would take a more active diplomatic stance against them - issuing demands of policy changes and threats of escalation, for example - and would react more dynamically to the state of the galaxy and a player's actions.

I also decided to try and help settle some debate that had been going on for some time; like repeatedly stated, I have always intended the Commonwealth to be "the good guys", especially in a world like that of Stellaris where atrocities are the norm. However, a huge number of people I discussed with refused to accept that position, either staunchly believing that all the morality flavor was simple pretext to justify military conquest, or that no empire (or its citizens) could actually truly care about harm befalling some random other empire across the galaxy. Also common was the assertion that it would only ever be practiced against "weak" targets, ie that no player would ever willingly pick a fight with a bigger empire.

That last issue was the easiest to address, and led to the creation of the direct combat bonuses the Alerans get when fighting the appropriate target. The ideological claims were more difficult, at first, but ultimately I settled on the creation of multiple branching event chains where the player would be forced to choose whether they wanted to act ethically, or act in the way they claim the Alerans would really want to, which would end up screwing over the player for being heartless or negligent. Over time, these grew into full story chains.