Disclaimer: I don't own Halo, the characters or the books, any new character that i introduce is my own...
Synopsis:
this is set one hundred years after the elite split from the rest of the covenant. Master chief I dead but before he died the human race was saved from invasion.
In the hundred years that have passed three factions have come to be the Sangheili alliance, the Covenant now only consisting of Brutes, Drones, Jackals and Prophets and the UNSC. All known Halo installations have been destroyed and the flood killed.
Here is a brief description of the three remaining factions.
Sangheili Alliance: After their betrayal by the prophets the Sangheili, Unggoy and Lekgolo formed their own government, let by the Arbiter. After taking back high charity from the flood they set about taking planets form the Covenant the Sangheili Alliance had a lot of victories in the opening few battles taking back and saving loads of their brothers and sisters. But after the disorganized Covenant forces came back to their senses a stale mate came to be, the Sangheili Alliance have never known peace as their own race.
Covenant: Though basically exactly the same as they have been for ages, the once mighty Covenant force has been almost shattered by it's forces tearing them self in half. In the opening few years of the Sangheili rebellion the Covenant forces suffered a countless amount of disgraceful defeats, they lost a load of planets and over half of their space armada to the dishonourable Sangheili. After calling their armies back from Earth they where able to force a stale mate between the Sangheili and them selves.
UNSC: The Human race was severely crippled after the Halo wars thanks to the Sangheili and master chief the human race was saved. In the hundred years the followed the Humans had time to re-build, they have developed hydrogen weapons and the Spartan V project was a complete successes. The Humans in their breathing space where able to re-build their empire and they now have legions of Spartans in their army and their Navy is big enough to rival the Covenant and Sangheili forces. The Humans have held back from the war between the Covenant and Sangheili and so have suffered no defeats or loses since the last Halo war. The Human army though equipped with Hydrogen weapons are still primarily using projectile weapons as they have been for the last thousand or so years.
Spartan V: The Spartan Vs are the result of long genetic and mechanical enhancements, they are 8-9 times as powerful and the Master Chief and their numbers are far greater spanning into the millions, the Spartans are the only troops in the UNSC forces permitted to use the new hydrogen weapons, bar the Navy. Hydrogen rifles are more complex and power fuller than the Covenant and Sangheili counter part the plasma rifle, it's only down side is that it over heads very quickly and is the same size as the battle rifle but I makes up for that by having a limitless no ammo cost as it draws in hydrogen from it's surroundings.