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.