When the Sieges ended, these balloonists chose to fly on, free now of the political delusions that reigned more than ever on the ground, pledged solemnly only to one another, proceeding as if under a world-wide, never-ending state of siege.
* * * * * * * * * *
There it is. The origin story of the Aeronautic Clubs. Everything down on Earth is terrible and they live in the muck and the grime and are full of sin and violence. But up in the heavens, up above it all, they are free to live a life of higher meaning. The "air" has become its own nation-state, having little to do with the ground aside from gathering information for the advancement of the cloud people.
"pledged solemnly only to one another"
I'm sure the Organizations and Clubs behind all these balloons are based on the ground. But where on Earth do such places exist? Islands, possibly. Mountain hideaways. Large floating platforms that never land! I suppose one must be in Eugene, Oregon, unless "Aeronautic Clubs" are different from "Organizations." You know, hobbies versus quite serious research, study, and probably wetwork.
"proceeding as if under a world-wide, never-ending state of siege"
In essence, the sky has become the final frontier (which makes sense seeing that Lindsay mentioned they follow the Prime Directive). In essence, a siege happens when the defender of an attack is unable to retreat. Up until fairly recently (in Against the Day's timeline), subjugated, oppressed, or people who felt under attack by the local religion or social mores or cultural traditions could flee, generally west. Westward expansion was the escape into freedom from a stifling status quo. But once the rest of the world was stolen by Western Civilization, these people had no place else to flee to for freedom. At that point, the entire world took on the never-ending state of siege. You would either have to fight or submit. But the balloonists found a loophole: the sky! They could escape the siege and begin a new territory with their own rules and regulations and religions! And that could be a paradise until their rules began oppressing other aeronauts and then they'd have to fight back or escape. But where would they escape to?! The moon?! Ha ha! Ridiculous!