Factions and Timelines in Gundam
In human history, we use different calendar systems such as BC and AD. Gundam consists of series that encompass different timelines or eras that represent our supposed future and have different calendar systems to differentiate those eras. Due to the lopsided amount of content in one timeline, called the Universal Century (abbreviated UC), categorizing Gundam various series has led to the distinction of being UC or not UC. The other Gundam series not connected to the Universal Century continuity are officially referred collectively as Other Centuries . English speaking demographics, however refer to these as "Alternate Universes".
Why is it important to know the existence of different timelines? Because the way mobile suits and Gundams are portrayed and used differ greatly, which affects their placement in competition due to aesthetics. While a majority of the Universal Century treats them as military vehicles, there are many other Gundam series where the mobile suits have the appearance of mechanical summons from a fantasy setting or are such an extension of its pilot that the Gundam itself visually could be mistaken as the hero on an adventure instead of the actual pilot inside. One of the most popular designs within the Gundam franchise is the Wing Gundam Zero (EW). It has angel wings, and this is normal for that particular setting. If you compare it against the FAZZ, there is a distinct difference in what modelers will intend to do with customizing their kits. But if you are unaware, as a judge you may negatively react to why a giant robot has bird wings, thus unkowingly impacting that entry's score.
Universal Century (UC)
The main and most expansive timeline of Gundam. The original Gundam series Mobile Suit Gundam takes place in the year UC 0079 and encompasses a conflict known as the "One Year War" (OYW) between the government of the Earth Federation and the Principality of Zeon, a cluster of space colonies who declared independence from the Earth sphere. From this first series numerous sequels and side stores were produced, either taking place during this particular period or father off into the future.
The following are factions seen during major points in the Universal Century.
Earth Federal Forces-(referred to as EFF, the Federation, the EFSF), the military of the Earth Federation- UC0079-to UC??
Zeon -Can refer to the Principality during the OYW, refugees from when the war ended, remnants of the Zeon faction in further eras of UC-(UC 0079-UC 0100)
Neo Zeon/Axis Zeon-upon the collapse of the principality of Zeon leadership after the OYW, many different flavors of Zeon would appear each proclaiming they were the true group to bear the Zeon name that was continuing the fight for independence or represented the true spirit of what Zeon wanted (UC 0087-UC 0096)
Titans-an elite autonomous counter insurgency group within the EFF intended to fight against Zeon remnants and terrorists that grew to immense power after UC 0083 that became itself an antagonistic force due to political corruption and Earthnoid supremacist agenda. (UC 0083-UC 0087)
AEUG-(Anti Earth-Union Group)-a group within the EFF, and also former Zeon soldiers and spacenoid sympathizers created to oppose the tyranny of the Titans, prompting the civil war within the EFF of AEUG vs Titans known as the "Gryps Conflict". The AEUG would also face off against Axis Zeon/Neo Zeon in what would be the first Neo Zeon War while the EFF was trying to reorganize itself from the civil war. (UC0086-UC0089)
The Sleeves -the remaining forces of Neo Zeon after the events of the Mobile Suit Gundam Char's Counterattack movie (called Char's Rebellion for the in-universe lore), they feature unique ornate markings on the uniforms and also on the mobile suits. (UC0094-UC0096)
Mafty-a terrorist organization intending to fulfill the failed mission in Char's Rebellion of forcing humanity off earth to allow its biosphere to heal from the repeated conflicts and pollution. (UC 0105-)
Crossbone Vanguard-the private military force of the Ronah Family that was created to be the force that protected the future nation of Cosmo Babylonia, a nation state ruled founded old era aristocracy traditions. It would fight the EFF in Gundam F91 and later have its name be appropriated and used by the heroic Crossbone Vanguard Pirates. (UC 123)
League Miltaire-a force created from current and former EFF and civilians to fight the Zanscare Empire that had invaded earth (UC 0149-UC0153)
BESPA/Zanscare Empire-a space-noid nation that in UC 0149 declares war against the EFF to completely eradicate the Earth's ineffectual government (UC 0149-UC0153)
The image below represents the list of animated Gundam works and year in the Universal Century that story took place. Compilation animated works that summarize or re-interpret their original source material have been omitted to avoid confusion.
Other Centuries and Meta Works
The "What ifs" of Gundam for alternate timelines and continuities. Depending on on how you were exposed to Gundam, you have heard these referred to as Alternate Universes. Because of the sheer amount of content in the Universal Century, it can be extremely difficult for a new person getting into watching the various animated works, especially since so many of them draw upon the One Year War from the first TV anime that aired in 1979. And so these other Gundam series were created to reach new audiences for the Gundam franchise, requiring no previous viewing of other Gundam works and are unrelated to each other (unless it's a direct sequel to one of these alternate series of course). Many of them are alternate takes of events that happened in animated works of the Universal Century, but could also vary wildly as various other parts of stories were explored such as
What if the opposing faction had Gundams?
What if the good guys were the bad guys?
What if the Gundam was a machine to organic human interface to fight rogue AI machines?
What if the story of the One Year Wars was just simply remade with different characters?
What if Gundam was a mafia show?
What if the OYW ended in a mutually assured destruction scenario with no side winning?
What if instead of world wars there was a tournament to decide which country ruled Earth every x number of years?
etc. etc.
Currently Other Centuries have these independent works, that may or may not have a sequel or some side stories:
Mobile Fighter G Gundam
New Mobile Report Gundam Wing
After War Gundam X
Turn A Gundam
Mobile Suit Gundam SEED
Gundam Reconguista in G
Mobile Suit Gundam 00
Mobile Suit Gundam Age
Mobile Suit Gundam Iron-Blooded Orphans
Mobile Suit Gundam The Witch from Mercury
(example of a Bandai Decal set featuring some emblems from various Other Century Gundam Series)
Gundam "Build" Series (Meta Works)
A more recent category appeared in the 2010s that is centered around believe or not, people building Gundam models. These meta works often feature tongue in cheek references and meta humor to both Universal Century and Other Century works as if the characters were like you and me, experiencing the fun of building and enjoying the nerd fights of being a fan. The one difference is that in these meta works, the characters are building a model that can be 3D scanned or coated with special particles allowing them to move, essentially building your dream Mobile Suit/Gundam and being able to pilot it virtually.