Gundam Unicorn

[Lord_Leperman]

Hathaway's Flash which happens in UC 0105 (Dunno the plot of this series) and the Gundam F90 in just prior to the events of Gundam F91. The last traces of Zeon show up in the latter under the banner of the Oldsmobile Army, AKA Mars Zeon (Zeon forces who exiled themselves on Mars after the OYW) who try to invade Earth through the use of a giant Rail Gun to bombard Earth (called the Olympus Cannon, as it's stationed above the mountain of the same name).

AFAIK Side 3 re-joined the Federation in UC 0099 or UC 0100 and no further Zeon activity was recorded after that (Besides Mars Zeon mentioned earlier).

For the sake of clarity, here are the events post UC 100 in chronological order:

105 - Hathaway's Flash (Novels, not 100% canon)
122 - Gundam F90
123 - Gundam F91 (Movie, canon)
133 - Crossbone Gundam/ Crossbone Gundam: Steel 7 (Manga, possibly canon since it ties in heavily with the F91 movie)
153 - Victory Gundam (Series, canon), Crossbone Gundam: Ghost (same status as Crossbone Gundam)
203 - Gaia Gear (Novels / Radio Drama)
223 - G-Savior (lol)