Time of Ending
The Time of Ending is one of the major time periods of the Imperium of Man. It was preceded by the Waning, stretching from mid-M41 to the end of M41. It is the "present day" of the 40k continuity.
The Time of Ending has seen the Tau emerge as a competitor, Tyranids nomnomnom countless planets, and the Necrons begin to awaken from their sixty-million-year slumber. Failbaddon is starting his 13th Black Crusade, an event that would surely be exciting had it not been covered in depth a decade ago. Lugft Huron rebelled in the Badab War and is becoming a major Chaos warlord himself. Rebellions are running like wildfire and the astropathic choir on Terra is constantly bombarded by pleas for help. The Adeptus Mechanicus has (once again) found an issue in the Golden Throne that they can't fix.
All in all, a bad time to be a High Lord of Terra.
Damocles Crusade
The first campaign between the Tau Empire and the Imperium of Man, eventually called off due to emergence of the Tyranids.
First Tyrannic War
The Imperium's first encounter with the Tyranids, which saw the Ultramarines First Company get nommed to a Marine and an entire world of Ultramar stripped of all life. We know most of you would be cheering the Tyranids on, but trust it, it's a bad thing.
The Siege of Vraks
As detailed in Imperial Armour Volumes Five, Six, and Seven, the munitions-stockpiling world of Vraks goes renegade under the guidance of the corrupt Cardinal Xaphan. The Death Korps of Krieg are called in to stem the rebellion. Seventeen years later, the siege finally ends with a full-scale Daemonic invasion and the intervention of the Grey Knights. Imperial forces still managed to have "won", spending countless resources to take worthless radioactive, chemically, biologically and Nurgle polluted planet back, while all the ammunition stockpiled on Vraks (the only thing worth fighting for) was spent during siege.
The Saint Cyllia Massacre
A whole Titan Legion suddenly switches to Chaos, blowing up the planet they were stationed on and disappearing into the Warp. Yes, this is just as hilariously Awesome as it sounds.
Massacre of Sanctuary 101
An Adepta Sororitas outpost is built upon a Tomb World, with the Sisters inadvertently waking up its sleeping inhabitants and giving the Ordo Xenos its first concrete confirmation of the existence of the Necrons.
The Badab War
Lugft Huron, Chapter Master of the Astral Claws, becomes too big for his britches and slowly builds an empire on the outskirts of the Maelstrom. He's eventually brought to battle after firing on Imperial vessels, leading to a massive, Space Marine-focused war. He's eventually defeated, flees into the Maelstrom, and starts heading the Red Corsairs.
Second War for Amageddon
Ghazhgkull Mag Uruk Thraka gathers one of the largest WAAAGHs ever, laying siege to the vital hive world of Armageddon. Much badassery occurs, especially on the part of Commissar Yarrick.