Vigilus is an Imperial Hive World located in Segmentum Obscurus. It is now the focal point of a massive free-for-all as the Imperial Forces there try to keep the planet from the hands of Orks, Eldar and Dark Eldar invaders from without, an insidious Genestealer Cult trying to subvert the planetary defenses from within, with finally Chaos madmen in the form of the Gellerpox Infected and their Death Guard masters joining the fun.
And then the Herald of Abaddon the Despoiler decides to come a-knocking...
About the Planet Itself
Prior to the opening of the Great Rift, Vigilus' main claim to fame (and indeed its main planetary export) was force field technology, specifically bastion-class fields, which were powerful enough to protect entire hive cities. Its own cities are enveloped by these fields, increasing the world's defensive capabilities.
Both the Adeptus Mechanicus and the Ecclesiarchy have a significant presence on the planet, the former due to an ancient treaty signed with the ancestors of the current ruling dynasty, and the latter heavily influencing the local PDF (named the Vigilant) as well as the Imperial Guard garrison. Not surprisingly, there are a lot of Sisters of Battle around to enforce the Ecclesiarchy's will.
Not surprisingly, the nobility, the Mechanicum, and the Ecclesiarchy don't get along too well, but have stopped short of outright civil war thanks to the efforts of the Aquiliarian Council, which is made up of more reasonable members of the three factions. That, and because A) the Mechanicus would butcher anyone who endagers such a techy planet and B) any Imperial force that starts a war against the planetary government would be considered renegade and blown up from orbit. The Imperium does not tolerate Imperial forces playing warlord. It didn't exactly go well for the Imperium the last time that happened. Times, really. Hell, one of the things keeping the Ecclesiarchy crazies restrained is the knowledge that if they got violent everyone and their pet rock would be screaming "Reign of Blood!". Which would be very bad for them.
Then, The Great Rift Happens
With the Fall of Cadia, Vigilus finds itself stuck on the north side of the Great Rift, in the Dark Imperium. What's more, the world's strategic significance rises exponentially when everyone realizes that it's located at the end of one of two known stable routes across the rift: the Nachmund Gauntlet.
Its hives still protected by the psychically-charged bastion fields, the world had become a staging area for any Imperial expedition daring to brave a foray into Imperium Nihilus (indeed, the survivors of the Stygies Front were using it as a rallying point), and the final safe harbor for refugees trying get out of it.
Vigilus is currently the focal point of the War of Beasts, a massive and ever-escalating conflict where the forces of the Imperium desperately try to defend it from Speed Freek Orks, Genestealer Cultists, Chaos madmen, two flavors of Eldar, Death Guard, and last but not the least, a Black Legion invasion with a Herald of Abaddon the Despoiler himself making an appearance.
Because of Vigilus' strategic location in Imperium Nihilus, the Imperium cannot afford to lose the planet, and as such is funneling more and more forces into the meat grinder, and this was before Abaddon's forces decide to step in.
Tl;dr- Vigilus is in all essence Kronus from Dawn of war but with actual stakes, as everyone has basically lined up to have a punching match with each other. Honestly it wouldn't be surprising for the Blood Ravens to show up, Gorgutz to be in charge of the Ork Waaagh and at the end of Harkens 80 day countdown, for Eliphas show up and start monologuing like a badass.
|The Planets, Systems, Regions and Sectors of the Galaxy|
|Imperial Homeworlds:||Holy Terra - Sacred Mars|
|Primarch Homeworlds:|| Baal - Barbarus - Caliban - Chemos - Chogoris - Colchis |
Cthonia - Deliverance - Fenris - Inwit - Medusa - Nostramo
Nocturne - Nuceria - Olympia - Prospero - Ultramar
|Planets:|| Armageddon - Cadia - Catachan - Ganymede |
Krieg - Kronus - Sacris - Sanctuary 101 - Scelus
Tanith - Tartarus - Vigilus - Vraks - Zayth
|Daemon Worlds:||Plague Planet - Sortiarius|
|Systems and Regions:||Solar System - Jericho Reach - Kaurava System |
Halo Zone - Stygius Sector - Taelus System
|Types of Worlds:|| Agri-World - Craftworld - Daemon World - Death World - Eldar World |
Forge World - Fortress World - Hive World - Tomb World