OK: the battle sequence in the series prologue compresses not only generations of story time but also the four most important events in the formation of the Trinity universe: the Red Mars Project, the Armageddon War, the First Return and the Second Return. Let’s see how quickly I can set them up for you.

In 2080, Earth had sent its first colonizing expedition to Mars--the Red Mars Project. The colony's scientists discovered a crashed alien ship on the Martian surface, which contained something of priceless value to the struggling Earthlings: an intelligent nanomachine (nicknamed "The Bacillus") designed to adapt any life form to the harsh conditions of Mars. Injected, it would instantly remake its host on the molecular level, giving enhanced strength, endurance and reflexes, and a much slower aging process to boot. (Presumably the inhabitants of the wrecked ship had been meant to use it, but their luck ran out too soon.) --The colony agreed en masse to be injected with the Bacillus, making them all essentially superhuman. Lives were saved, and all was well until Earth found out about the discovery. Then all Hades broke loose: everyone wanted a shot of the Bacillus, no one could agree who owned or had the rights to it, and the quarrel escalated to all-out world war. This was the Armageddon mentioned in the prologue.

A party of the Mars colonists decided to travel back to Earth and offer their help in rebuilding civilization: this was the First Return. This went well at first, but gradually they found that their new metabolisms, adapted to Mars, began to mutate under the influence of Earth's different environment and strong ultraviolet radiation. They couldn’t bear the daylight, and the Bacillus began to consume their red blood cells, forcing them to replace them somehow…in short, on Earth they turned into classic vampires. They considered themselves a new, improved type of human, stronger than the weak Terrans, and took the name "Methuselah". The already weakened Terran populace now had to fight off a new threat, and civilization was on the brink of total collapse.

Back on Mars, no one could agree what to do next. The colony's leaders--a quartet of lab-created, genetically altered genius-warriors--were divided; three of them bitterly resented having been created only to serve, but the fourth [the chief scientist] still felt bound to Earth and humanity. Faction fighting broke out, and the rebellious three led the Second Return to Earth, which was intended not to help, but to take advantage of Earth's crisis: to conquer the planet and make it a world of vampires. And THAT is the battle that's shown in the prologue to episode one.

Right--all this takes place before the series even begins...