(ゾイド)星人 (Zoid) planet-people -> Zoidian(s)
ゾイド星 Zoid-planet/Planet Zoid -> Zi
Earth tribe is 地底 depths of the earth, not just 地 earth, but that looks funky when all the others are one-word names in English. I suppose you could also use "Subterranean"...
Otherwise, corrections/forks in head/thoughts on names are welcome. The original text can be found here.
Zi is a planet shrouded in mystery.
And now it enters a hundred years of war...
The secrets of its birth are still mainly shrouded by a veil, with many portions unknown. Though in the modern age the clarification of biology, evolution, and the like has greatly advanced, the study of history still leaves most things unexplained. Great areas of this planet have experienced major earthquakes, volcanic eruptions, and changes in the crust on countless occasions. That is: thwarted by the various works of nature and the universe, history was not handed down, and instead was buried under lava, coming to be known only to the depths of the earth. Now, the history brought to light here is therefore no more than three to four hundred years old. And it is a history of battle stained with blood...
The age of tribes
Approximately 50 tribes lived scattered far and wide over the central continent of Zi. Each tribe, adjusting to their environment, made use of everyone's/each person's mecha, hunted, and grew crops. The notable tribes were ones like the bird tribe living in the central mountain range, the sea tribe dwelling in the ocean, the sand tribe existing in the desert, and the earth tribe dwelling underground in the deep depths of the earth. Their reason for living in self-sufficiency and isolation lay in the ever-changing natural disasters. Moreover, because there was enough food and water in each territory, nobody went outside their own region. Rather, it was a way to defend themselves.
But from ZAC (though almost the same as the Earth's Christian calendar, because Zi's diameter is a little smaller in comparison to the Earth's, its rotation time is faster, putting this date about 7-8 years forward) 1600 on, Zi maintained an eerie silence, and though small-scale volcanic eruptions were seen, when it entered the 1700s these too fell dormant.
The age of territories
Around 1850, tribes with mutually insufficient abilities supplemented each other, aiming at increased food production, and community bodies started forming. The lessons the Zoidians had unconsciously learned in their battles with the harsh environment-"nature is the enemy" and "Zoidians and animals are friends"-were put into practice. Before long, the peaceful integration and union among tribes progressed, domains spread, and small countries (territories) formed.
But this peaceful time didn't continue for long. While territories possessing excellent abilities kept absorbing other countries and becoming powerful, weaker territories resisted it; scrambles for the domain of large countries started up; and tragedies like the breaking up of one country from family quarrels became a frequent occurrence.
The age of civil war
No sooner than they'd entered the year 1900, the strong Zoidians' fighting and theft of mecha became routine between territories. Then the main countries began to modify the mecha they'd used only for hunting and transportation to carry weapons, and there was no stopping things now. If the remodeling contest intensified in violence through what was becoming a constant desire to use these mecha, the border skirmishes becoming incessant -- it foreshadowed the all-out war that would soon start.
Before they knew it, the Zoid central continent was split into two great powers. On one hand were peaceful allied forces that hoped for a peaceful solution through politics, mainly led by Helic (the patriarch of the Wind Tribe); and on the other was a federal army that made their leader the combat sect Guylos (of Earth Tribe lineage) who harbored ambitions to conquer the continent from the depths of the earth.
The Zoid continent devoted its time to the ebb and flow of offense and defense; women and children were wounded because of the war; treachery, double-crossing, and coup d'etat broke out between territories; secret information flew this way and that; Zoidians' hearts were disturbed; and this planet, once filled with peace and love, was changing into a planet of suspicion and betrayal.
Helic was troubled by the hardening of Zoidians' hearts, the burnt greenery of the continent, and the figures of innocent children who tried to escape, and gradually began to hold doubts about the fight for peace he'd imposed on himself.
The age of nation creation
Only a hundred years ago this planet's greenery grew thickly, flowers bloomed wildly, love ruled all, and strong hatred was subdued with this splendid love. This planet that should love was filled with the stench of gunpowder and blood...
Unexpectedly/one day, the poet/private Helic left the Central Continent operating a small mecha (a bird-type Zoid) without informing his subordinates. The time was the year 1955.
The peaceful allied forces Helic left behind set up a dummy general and kept his absence a secret, withstanding frequent attacks from the Guylos faction. One and a half years passed, and one day, as summer set in on the Central Continent, its skies were covered with battle mecha they'd never seen before. The unknown beings that rode these unknown mecha began an attack on the Central Continent without warning. The Zoidians, exhausted from the long wars and at their wits' end, could only run away in confusion. They had no power and such left to fight with a foreign enemy. However, Guylos and his sect alone encouraged the Zoidians, fighting the foreign enemy skillfully. The continental army, which had seemed to crumble in one blow, endured the violent assault, gradually collected into one, and even began to counterattack.
Thus, the day after thirty had passed, one wounded bird-type mecha landed at a continental army base. Appearing from the cockpit...was Helic.
"Guylos, the opponents we should fight are the foreign people who aim to take this rich continent. I have traveled long - Zi is huge, and the universe surrounding this planet is magnificent. We are no more than small beings living on a small continent. We will no doubt lose everything while engaged in these petty disputes. Open your eyes, Guylos!"
The Zoidians wrapped up in said petty disputes recalled the lesson left behind by their ancestors -- "Zoidians and animals are friends" -- and gathered together behind Helic. All the tribes united as one, and confronted the foreign enemy. Helic stood at the head of the whole army:
"Listen, Zoidians -- this foreign enemy attacking us came from a cold country. Their weakness is the heat. The summer they fear most arrives quite soon. Until then, we can but endure."
Guylos was not an ambitious person who saw nothing but conquest by any means. Now he realized what he should do, and supported Helic's command, often bringing together tribes, encouraging soldiers, and standing in the lead with Helic recaptured the continent's skies from the foreign enemy at once.
And then it was ZAC 1956, the seventh month, the twenty-fifth day: the summer solstice. The continent's temperature rose exactly 10 degrees from that day. Morning came. There were no figures of enemy mecha in the red summer skies. The foreign enemy ceased to exist in one morning.
Peace returned to the Central Continent.
The Age of Democracy
Guylos swore loyalty to Helic, promising to use his abilities only for peace and rebuilding the ruined continent. The Zoidians respected their benefactor Helic who'd rescued the continent like a father, and accepted him as king. Here was the birth of the Helic Republic. The king laid out a democratic political system -- assemblies were held, everything decided by discussion, and each tribe treated equally. The Zoid continent regained the peaceful days of before.
King Helic married, and was blessed with a child. The child was Helic II. And the king took another bride - the child who was born with that woman was named Zenebas (later Emperor Zenebas).
Helic II's mother, in coming from the Janice house (a peace-loving noble family of the wind tribe), descended from blood that excelled in political strength. To prepare for the return of the age of hateful conflict and the foreign enemy that the continent confronted before, his father bore the child Zenebas with another person. Zenebas's mother was a younger sister of Guylos, descended from brave soldiers. By dividing his blood in two, King Helic thought to protect and match both brothers' strength in a national policy of both the pen and the sword (politics and military force). Their father explained the necessity of military power to Helic II, and instructed the younger brother Zenebas in the importance of politics.
At the age of 78, King Helic left this world.
In ZAC 1975, Helic II was 18 and Zenebas 16.
The king left one letter to both children.
 戦闘派ガイロス. Is this a title, a membership? I don't know. I suck.
 Kanji say 詩人 poet, 私人 private man (same reading, しじん) makes more sense there. Typo? (like I can talk...)
 ジェナス = Janice? Janis? Jenice?
What is it with this book and people leaving behind letters before they die? Though one might not want to write King Helic off as a crazy hippie with a Shoteagle yet, considering the contents of said letter...yeah, working on that.
(edit) This entry seems to be getting spam, but I want to leave comments open to non-registered users. So: anonymous comments are now screened and will show up after I check 'em out. Sorry about the delay, legit commenting-people.