The planet Zi and its ion-rich oceans gave birth to a large number of metal life forms. Some went on to become the humanoid Zoidians. Others became the creatures known as Zoids, mechanical living beings with a core as a central life-force.
For centuries, the Zoidians lived in small tribes with an emphasis on survival, as their planet was wreaked with earthquakes and volcanoes. As the tectonic instability quieted down, their numbers grew, and people had time to squabble over territory. They took and modified the wild Zoids of the planet, eventually altering and changing them into massive war machines. In ZAC 1955, Helic Muroa of the Wind Tribe, who had tired of the constant battles, united the fifty tribes of the Central Continent into a single nation. He managed to convince his rival Guylos (of the Earth Tribe) to ally with him as well.
Helic's two sons, Helic II and Zenebas Muroa, inherited his nation after his death in ZAC 1978. Zenebas favored aggressive foreign policy, preferring to attack first and ask questions later in contrast to his brother's more peaceful approach. Tensions mounted, and he left after a bitter quarrel and framing by the Republic assembly, splitting the continent into two groups; the Helic Republic in the east and the Zenebas Empire in the west. The two nations went to war in ZAC 1980, beginning a series of low-scale conflicts.
In ZAC 2029, a ship from Earth, the Globally 3, crashed on Zi in the middle of the Central Continent. The survivors joined both the Empire and the Republic, using advanced Earth technologies to increase the war potential of the Zoids. The intensity of the war increased, as new Zoids like the Gojulas and Iron Kong were deployed. The two sides battled for nearly a decade, until the Republic deployed the super-heavy Ultrasaurus. With the Ultrasaurus, the Helic Republic was able to defeat the Zenebas Empire.
Emperor Zenebas himself fled, traveling to the Dark Continent of Nyx. Once there, he made a bargain with the emperor of the Guylos Empire to rebuild his army. In ZAC 2042, he returned, invading the Republic with a force of new Zoids. The Zenebas forces quickly advanced with the rollout of the Death Saurer in ZAC 2042, crushing the capital of the Republic. The Republic's government survived, and planned a counter-offensive in the midst of guerrilla warfare in the mountain ranges. In ZAC 2048, they deployed a new Zoid, the Madthunder. With the new Zoid, they were able to defeat the Death Saurer armies and destroy the Zenebas Empire.
Zenebas fled again, but before he could reach the Dark Continent, the forces of the Guylos Empire ambushed him. His army and its Zoids were absorbed into Guylos', who started a new series of conflicts with the Republic. After a successful landing and a long offensive through the brutal terrain of Nyx, the Republic army faced Guylos' trump card, the incredibly powerful Gilvader. To defend itself, the Republic created the Orudios and finally the King Gojulas, a monstrous Zoid that spearheaded a final offensive.