The nation of Zeon is a government entity that plays an important role in the Mobile Suit Gundam Universal Century timeline. The nation came into being when Zeon Zum Deikun, the ruler of the space colony Side 3, declared independence from the Earth Federation.
The Republic and Principality of Zeon
In the year U.C. 0068, Deikun was assassinated by the Zabi family, which quickly took power and rechristened the republic the Principality of Zeon. The Zabi family ruled Zeon until the end of the One Year War in the year 0079. For the majority of this era, the nation was ruled by Degwin Sodo Zabi. However, after Degwin's son Garma was killed during the One Year War, he decided to pursue peace negotiations with the Earth Federation.
Degwin's eldest son Gihren Zabi, however, disagreed with his father's methods, and using his gifted intellect and skillful oration, was able to assume true power. Degwin did not think highly of Gihren, and at a point even compared him directly to Adolf Hitler. When Degwin was en route to begin the peace talks, Gihren assassinated him.
However, Gihren's own reign was not long-lived, and ended shortly before the conclusion of the One Year War. His sister Kycilia Zabi killed him out of revenge for the murder of their father. She then assumed control of Zeon's forces during the Battle of A Baoa Qu.
The battle proved to be the Principality's last stand. With the war on the verge of being lost, Kycilia attempted an escape, but she was killed by Char Aznable out of vengeance for the death of his father, Zeon Zum Deikun, over a decade earlier. With the death of the last ruling Zabi, the One Year War ended and Zeon fell apart.
At the end of the One Year War, forces still loyal to Zeon retreated to the asteroid Axis and formed a new colony. Shortly thereafter, Haman Karn established herself as ruler under the pretense that she would relinquish power to Mineva Zabi, the last of the Zabi family, once she had come of age. However, Haman's true objective was to use Mineva as a puppet to rule behind.
In the year 0083, other remnants of the Zeon forces, the Delaz Fleet led by Aiguille Delaz, attempted to provide Zeon with the strength to come back by enacting Operation Stardust. The goal of the operation was to reduce the Earth Federation's military forces, complacent with their victory in the One Year War, to nothing in one fell swoop. To that end, they stole a prototype Gundam armed with a nuclear warhead and used it to annihilate a large portion of the Federation's fleet as they were off guard and conducting a naval review. The final stage of the operation involved dropping an abandoned colony on Earth.
Delaz's plan was foiled by the combined efforts of both members of the Earth Federation pursuing the stolen Gundam and a traitor in his own ranks. Cima Garahau, ostensibly working for Delaz, was in fact a turncoat secretly working with corrupt Earth Federation military officials looking to stage a coup. Delaz's plan to restore the Principality of Zeon ultimately failed, though Cima was also killed, unable to complete her own objective. However, the disastrous showing of the Earth Federation to prevent the theft of a Gundam, the decimation of their fleet, and the destruction wrought by the colony drop allowed the corrupt ranks of the Federation military to form the Titans.
In 0087, a civil war broke out between the Titans of the Earth Federation forces and the AEUG, a resistance fighting for the goal of relinquishing the Federation from the Titans' grasp. Both sides saw the Axis forces as a potential trump card and attempted to negotiate with them. Axis initially sided with the Titans after old wounds reopened between Haman and Char, who after living on Axis for a time left to join the AEUG. However, the AEUG managed to succeed at later negotiations and brought the Axis to their side.
The civil war ended with the destruction of the Titans and the loss of numerous key AEUG pilots, while Axis emerged from the conflict mostly unscathed; through their negotiations with the AEUG, they had also regained Side 3. Haman used this opportunity to establish Neo Zeon and fought the Federation for control of the Earth Sphere. However, Haman's warring faltered with the insurrection of her officer Glemy Toto. With Neo Zeon's forces split, the movement ended when both of them were killed at the end of the war.
Second Neo Zeon
Though he was thought dead following the end of the Earth Federation civil war, or the Gryps Conflict, in 0088, Char Aznable established a second Neo Zeon in 0093. Char's singular goal was to reduce Earth to an uninhabitable state, forcing humanity's total migration into space and accelerating the development and acceptance of Newtypes. However, Char's plan was foiled, and he was defeated in his final battle with Amuro Ray; his adversary dating back to the One Year War.