Gate: Thus the Sons of Sanguinius fought there

Chapter 0 - Prologue

A dim light filled the street of yet another hive city district, the citizens were going on peacefully with their days in the Imperium of the 43th millenium. The lives of average citizens had became much better since the recent victories against the ruinous powers.
The general situation of the Imperium of Man was getting better too. Heretics and Xenos alike had been pushed off humans world by the relentless attacks of an empire that was starting to take back what was rightfully it's propriety.

To speak of great events, a great hero had returned to the Imperium. A hero who is none other that one of the mighty primarchs, a son of the Emperor himself. The one to return was Lion El'Jonson, who awoke from his millenia old slumber to defeat the chaos servant known has Abaddon the Despoiler. The Lion led an all out assault against the 14th black crusade of the traitor, which eventually led to the doom of the the Despoiler and a large portion of the Black Legion in the 239 year of the 42 millennia.

The Inquisition, had declared the High Lords of Terra heretics for reasons that are still kept secret from the masses, and only known by a few persons across the galaxy. The High Lords of Terra defended themselves and a civil war soon happened between the two major human factions that were the Inquisition and the rest of the Imperium armies (spaces marines chapters did not take part in this civil war, except the Ultramarines and the Dark Angels who both fought with their Primarchs against the Inquisition), ending in the victory of the High Lords who decided to reform the Inquisition entirely, supressing notably the infamous privilege to declare exterminatus upon a world without being authorized by an astra militarum commander, or a similar title of another Imperium force.

Everything has started to get back on tracks, humanity had finally stopped it's downfall and men didn't have to fear their own brethren anymore. It's not a new Golden Age, but they are slowly getting there. But the Imperium was still not safe, as traitors and heretics still existed, tyranids Hive-fleets continued to arrive every few centuries or millenium, Dark Eldar raiding parties continued to pillage defenseless worlds across the Imperium, and orks WAAAGH still infected a number of worlds as well as the occasional Dark Eldar who kidnapped some humans for their sick and twisted endeavors.

The Codex Astartes had been modified once again by Roboute Guiliman with the help of the Lion, as the threat of Chaos was now almost non-existant, allowing the chapters to grow to 2'500 space marines instead of the previous limit of a 1'000, reinforcing significativly their fighting forces. Furthermore, the Astartes and Primaris had been modified so that their bodies would stay healthy longer, allowing a few veterans to go past the thousand years.

Many thing had changed, but let's focus on the sons of  Sanguinius. After the tragedy of the devastation of Baal by the Tyranid Hive Fleet Leviathan, the Blood Angels and their successors chapters, or at least what was left of it, were given time to regrow their strength and rebuild their world as they were decided to not be fit for immediate combat by the Primarch Roboute Guiliman who had flown to their rescue in the wake of the Indomitus Crusade. The carnage of Hive fleet Leviathan had ravaged both of the moons and a large part of Baal itself. But despite such carnage, the Blood Angels did not relocate their forces to another world, more suitable for recruitment. Instead, they helped the survivors to rebuild cities, and with the help of the Mechanicus, terraformed to a small scale the surface of Baal to resemble what it once was long ago, before the coming of the Primarch Sanguinius. The moons however, had been drained of any biomass and were as such, impossible to terraform properly, instead large domes were built to allow human life on the twin moons. Angel Fall became a thriving Hive City, the once mutated and weak population of the wastelands of Baal had regained their strength as humans, once more ressembling the natural state of humans instead of malnourished scavengers. Monuments in the honor of the Angels had been erected and in the two millenia that followed the tragedy, nothing bad happened to Baal, Angel Fall, or it's population.