Kronus II lies within the lost Kronus System. It becomes a battleground for domination. Coming out of the ground was the Necrons, hiding underground there. Then the Forces of Chaos came to turn this world into a chaos world. Coming in from the Imperium was the Imperial Guard, coming to reclaim all worlds the Imperium had. Then the Space Marines came to liberate this world from the heretics, xenos, monsters, and zealots. The Eldar, the ones responsible for their treachery on the 2nd Cadian, hides within the surface of Kronus II, while the Dark Eldar has planned to destroy those. The Hive Fleet of the Tyranids came in to turn this world into a harvest world for their purpose of consuming all forms. The Sisters of Battle of the Imperium came in order to turn this world into a sacred privilege. Then the Tau Empire, who are the ones holding this world as their colony, were planning to eradicate all these factions coming to conquer this world. However, forces of the Fourth Military Expeditionary Force, an element of the Amareican Military Expeditionary Fleet, who had a base frozen within the Kronus System, were actually the first to arrive here. And finally, the Ork forces came to have this world their biggest world for their campaign.
The Kronus System, once a system of the Imperium, becomes a deserted system and a battleground for domination. The 1st Cadian Shock Trooper Regiment under the command of General Storm Hammer has been sent to find an Eldar responsible for her treachery back in Tanith. However, the 1st Cadian find something than they ever prayed - they have found ice which was encasing unknown personnel, vehicles, aircraft, and others they didn't know.
The techpriests then begins to remove the ice which all the 1st Cadian didn't know...soldiers of the Fourth Military Expeditionary Force of the Amareican Military Expeditionary Fleet. Upon thawing all of them, one of them - an alicorn - tries to get up only for him to fell back to the ground. General Hammer has informed Segmentum Command all of these, where they issued him new orders. They are to take them to their base in order to know how they are here.
After hours of interrogation they find out that they were the first to arrive, where as the Tau Empire arrives as the second. However, the Blood Angels and the Order of the Scarlet Rose came, engaging the heretics. This caused the 4th MEF merged/integrated with the 1st Cadian permanently. The Blood Angels warned Storm Hammer to leave, but he refuses because Segmentum Command issued him the orders. The Order of the Scarlet Rose also warns them that they will make this system a sacred privilege, which angers the 1st Cadian.
This caused the Kronus System Crusade to begin, which started with the Order of the Scarlet Rose, the Blood Angels, and the 1st Cadian forces attacking, where as other factions joins the Crusade for the domination of the Kronus System.