The Republic of Zeon (ジオン共和国 Jion Kyōwakoku?) is a nation featured in the Mobile Suit Zeta Gundam television series and the Mobile Suit Gundam Unicorn OVA. It existed before the Principality of Zeon and later would become its successor state.
In U.C.0053, Zeon Zum Deikun was appointed Prime Minister of Side 3. On September 14, U.C.0058, Side 3 declared independence and established the Republic of Zeon. In U.C.0068, Deikun suddenly died of a heart attack during a parliamentary speech. When Degwin Sodo Zabi took control, he wiped out the opposition and abolished the Republic on August 15, 0069, and declared a transition to a monarchy. The Zabi family, having gained power, aimed for independence from the Federation government by force. On January, U.C.0079, the Zeon War of Independence (One Year War) began. With the destruction of the Zabi family during the closing stages of the One Year War, the Principality of Zeon transitioned to a Republic just before the end of the war and returned to its name of Republic of Zeon. During the First Neo Zeon War in U.C.0088, Side 3 along with the Republic, came under control of Neo Zeon and would eventually be liberated by the AEUG and Federation fleet after the self-destruction of Neo Zeon.
Following the One Year War, the Republic of Zeon was created with a pro-Earth Federation government led by Darcia Bakharov. Although regarded by some as a Federation puppet government, the Republic had been granted a degree of autonomy. However, the Federation planned to dissolve the Republic by U.C. 0100, which would cause the name of Zeon and his Newtype theory to fade into obscurity. Republic of Zeon defense minister Monaghan Bakharov would devise the Co-Prosperity Sphere plan and sponsored the Neo Zeon remnants movement, known as "the Sleeves", led by Full Frontal to continue the fight for Spacenoid independence. When the Vist Foundation offered them Laplace's Box, an enigmatic object that had the power to topple the Federation government, Frontal intended to use it as a time saver to forestall the dissolution of the Republic so it could help in the formation of the Side Co-Prosperity Sphere, which would boycott the Earth, forcing mass space migration and causing the Federation government to collapse. However, following the defeat of the Sleeves in the Third Neo Zeon War, the Republic of Zeon retired their independence in U.C. 0100 and was folded back into the Earth Federation.
- Originally, "Republic of Zeon" was the name of the Principality of Zeon's successor after the end of the One Year War. According to Mobile Suit Variations, the pre-Principality government was simply called "Side 3 Republic". However, since Mobile Suit Variations was out of print for a long period of time, this information was lost, and the pre-Principality government was referred to as "Republic of Zeon" as well in later sources.
- The fact that the Republic of Zeon gives up its autonomy in U.C. 0100 was first established in the "Official Universal Century Timeline" published in Dengeki Comics mangas starting from 1994. However, for a long time, the reason for this was not explained, save for in the non-canon manga Mobile Suit Gundam in UC 0099: Moon Crisis. Eventually, Mobile Suit Gundam Unicorn established that the Republic of Zeon agreed to to return its autonomy in U.C. 0100 when it signed the peace treaty with the Earth Federation.