Baal
Baal is a radioactive wasteland of a Death World, famous for being the home of the Blood Angels, the most badass vampires in history.
The Blood Angels' Primarch, Sanguinius, fell upon Baal Secundus after he and his brother Primarchs were scattered across the galaxy by the machinations of the Chaos Gods.
Overview
Baal has two moons, called Baal Primus and Baal Secundus. Apparently, the moons were pretty damn close to some Paradise Worlds, with cultures comparable to High Roman Catholic nations but the Age of Strife slightly altered that. With nukes. By the time of the coming of Sanguinius, Baal and its moons were a Mad Max wonderland dominated by a tribe known as The Blood and foul Mutant hordes. Thanks to the effort of Papa Sang, the mutants were defeated and the people of The Blood came to ascendancy. Later during the Horus Heresy, Baal became a central loyalist hub under the control of Warden Arkhad. Many members of the Shattered Legions took refuge on Baal.
The moons' populations now spend their time trying to evolve out of the Stone Age.
Or they did, until the mother of all clusterfucks ensued. Baal Secundus is still more or less intact thanks to the intervention of our Spiritual Liege (and when we say intact we mean "utterly trashed by the nids but extensively terraformed to go back to the days of the paradise moon of ancient times"). In a rare instance of Noblebright, Papa Smurf promised to Dante that he would reconstruct Baal and its moons to its pre-Age of Strife paradisal state and in a rare stroke of common sense, told Dante that part of the reason why Chaos has worshippers is because the average Joe already lived in hellholes, so joining Chaos wouldn't make a difference. By making all worlds in the Imperium as livable (Including Baal), it would deny Chaos any free PR to tempt the denizens of the Imperium. As of the Indominus Crusade, it has been terraformed back into its paradisal state before the long night on the order of Robu. Baal Primus, on the other hand, is now completely bereft of life after Ka'Bandha showed up to flip off the Hive Mind.