We have good evidence that, one a lot of the people that went in to space to live in the Colonies did so willingly and that the Sides were a part of the Federation Government so I don't see the Imperialist organization angle from since it was the government of a United Earth that started buliding the Colonies in the first place so it's not like they came in one day a took over when they were at the top of the Government structure to start with. Even after the Republic of Munzo was created and Side Three was basically independent the Federation was hands of for years when it came to trying to get them back in the Federation fully and the Military build up only start after the Zabi's took over and start building a army. The only place that the Contolist movement was a Mass Movement was Side three and if things were bad in the rest of the Colonies that you would have had more then just Side Six's attempts to be neutral for two year before the One Year Wars start and during the Conflict. Two I would not call it a Slow Decay when even after all the loses of the One War it took Star Dust happening for the Titans to come about and they were so extreme that a good portion of them just out right quit serving the Government to follow Jamitov no matter what he did including making deal with the Zeon Forces the Titans were supposed to be fighting.
1. We also have evidence that plenty of people
didn't go willingly. There's a whole subplot of old folks among the Side 7 refugees in the very first arc of the first show who mistrust the Federation government for forcibly deporting them and leap at the opportunity to return to Earth thanks to the extenuating circumstances of the whole White Base situation (also literally threatening mutiny to do so). Forced population relocation is imperialism, full stop, and it's something that the Federation quadruples down on over time and is made far more explicit in supplementary materials. Is it the worst thing to ever happen, no, but I'm not going to sugarcoat it when giving a summary of why the OYW happened, because while the Zabis escalated a situation to WWIII with radical rhetoric, there was still a situation for them to escalate in the first place, and Space Separatism (which is separate from Zeon Zum Deikun's far more
esoteric ideology of Contolism before the start of the OYW) existed before and would continue to exist long after.
2. Operation Stardust was the justification used for the creation of the Titans, yeah, but consider that Jamitov and Basque Om were already high up in EFF command and were just looking for an excuse to go full ethnic cleansing on the Spacenoids. "It took Operation Stardust for the Titans to come about" is true on a surface level, but everyone involved in founding the Titans was already a respected officer in the EFF.
I can also point out that after U.C 0100 things were peaceful in the Earth Sphere and things started to improve again with new Colonies being built and no one blowing shit up on Earth. Then the Crossbone Vanguard stuff happened followed by the Jovian, and then Zanscare started as some kind of Cult inside the EFF's SNRI division and then decided to start blowing everyone's shit up. It's Kind of understandable after every thing that happens in the timeline the Federation is a shadow after Victory and things are kinda shit for everyone.
3.
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4. Everything set after UC 0105 is a picture of an Empire (the Earth Federation) falling apart and losing its authority over the outlying territories (the space colonies) through simple decay of material resources (and also the constant war and the events of Unicorn and Hathaway's Flash probably didn't help). One of the main recurring plot points in F91, Crossbone, and Victory is that the Federation can manage maybe a single fleet battle in each, with actual resistance to the fascist space empire du jour falling to deserting officers and citizens' militias. This entire segment of the setting is what I mean by "a long decay", although you can definitely say that the EF also just never recovered, in material or morale, from the OYW.
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