For the most of the story set with the Universal Century are either in the twilight(no pun) hours of the war or it's end, I mean beside from the first show we have animes, games, mangas and movies that could give us a better starting point for examples let's look at "Mobile Suit Gundam: The Mane Invasion" by awkwardGardener while the way they had done it is great it would had been better if they would to use Mobile Suit Gundam Thunderbolt: December Sky not only would the Mobile Armada of New Equestria gain the ruins of side four but tech of both Earth Federation Forces Moore Brotherhood and Principality of Zeon's Living Dead Battalion which means thanks to the Psycho Zaku Unicorns and maybe Pegasi could use their magic while in suit, the Earth Federation and Zeon would not only be out number by ships but also their suits would be out gun give Pegasi can change the weather at will as the spells Unicorns can use well you see where I'm going with this.

My point is there are many possible setting to use from the One Year War so please keep that in mind