Zeon is an inhabited planet with a ring system in the M34 Alpha star system. Zeon And Ekos the two class M planets in the system. The total population of the two planets was 16.1 billion.
Zeon is further out from its primary than the sister planet Ekos. It is the homeworld for the Zeons, a humanoid species.
In 2268, Zeon was briefly endangered when the Ekosian National Socialist Party Nazi regime planned to attack it with a fleet of manned and unmanned weapons. Promoted as the "Final Decision", the attack was barely averted by the crew of the starship USS Enterprise NCC-1701, working with the Zeon and native Ekosian anti-Nazi underground resistance. (TOS Patterns of Force)
After the close call in 2268, Zeon became a staunch Federation ally and later member world. Zeon has tough and dedicated defense force. Zeon has a few modern Starfleet ships and several older ships that have been modernized. Their sentimental Favorite is ZDF James T. Kirk, a modernized Constitution class Starship.
Ekos and Zeon maintain a tense neutrality towards each other in their home system. Neither wants the devastation an in-system war would entail. But that war is what each side primarily trains for.