The original Gundam universe is set during a war between the Earth Federation and the Principality of Zeon. The Federation rules the world. The Principality of Zeon is a group of space colonies that seek independence from the Federation and the establishment of a nation that they believe to be the next step in human evolution.
The Gundam used during this war, better known as the RX-78, is the secret weapon of the Federation developed in response to the Zeons' robot weapons known as mobile suits. The RX-78 stands 18 meters tall with a 9-meter tall titanium shield. It has two Vulcan cannons mounted on its head and several weapons, most notably a rifle and sword, powered by what are called "Minovsky Particles."
Numerous sequels in this universe occur during and after the Federation's war against the Zeon, with the newer Gundam models retaining a similar base design with slight chassis changes and new weapons such as atomic bazookas and detachable independent lasers operated through psychic powers.
The first Gundam series not to use the original universe was G Gundam in 1994. This series took a radically different plot line, putting the Gundam robots as the tools of martial artists representing different countries in a tournament to rule the world.
A year after G Gundam concluded, the franchise rebooted again with Gundam Wing. Here, the Gundams are a set of five robots developed and operated by rebels seeking freedom for the Earth's orbiting space colonies. Compared to the original series' Gundams, the Gundams in this series are generally depicted to be much more powerful, although they share a similar facial appearance, even after their upgrades in the movie sequel.
During the latter half of the 1990s, the Gundam franchise introduced two more universes: Gundam X and Turn A Gundam. Both take place in a post-apocalyptic world after a war similar to the one portrayed in the original series. These Gundams bear a resemblance to those in Gundam Wing, with the Turn A Gundam portraying the Gundam's usual forehead "V" underneath its chin.
The 2000s saw three new universes introduced to the Gundam franchise: Super Deformed Gundam, Gundam 00 and Gundam SEED. Gundam 00 and Gundam SEED take elements of earlier series in a new light, with 00 copying the role of the Gundams as a force against an oppressive status quo as portrayed in Gundam Wing. The original series' eugenic overtones are echoed in Gundam SEED. However, the Super Deformed Gundam series takes a significant shift as a parody, portraying the Gundams as autonomously functioning robots that are the size of children.