The Southern Empire

As described in the Shadowborn novel, the Southern Empire is an outlander land from the same world as the Great Kingdom of Avonleigh. This unnamed outlander world is thus where the Shadowborn family originated. The Southern Empire and the Great Kingdom held some amount of animosity against each other due to the conflicts of the Heretical Wars  and maybe the War of Evil. In addition, the Southern Empire followed deities judged heretical by the Church of Belenus, the dominant religious power in the Great Kingdom.

History

Not much has been revealed about the early history of the Southern Empire in canon sources. In the time of Kateri Shadowborn, a hero of the Great Kingdom who fought the Southern Empire in the Heretical Wars, the Southern Empire was ruled by Grand Caliph Muhdar ab Sang. At least according to Lysander Greylocks, the grand caliph was wise and benevolent ruler until he encountered the fiend Lussimar, also known as Ebonbane. The fiend approached the Grand Caliph as he was praying to his god for advice on dealing with the Sea Raiders of the far north. Taking on the guise of Muhdar ab Sang's deity, Ebonbane corrupted the caliph and drew him mad. So possessed, the caliph ordered the events that caused the Heretical Wars with the Great Kingdom. In addition, the Ahltrian, previously an order of adventurers and explorers serving Grand Caliph ab Sang, were changed to a secret society of murderers. Those who objected or found the truth were quietly murdered. Upon the orders of the Grand Caliph, the Ahltrian personally oversaw the sacking of Letour and Sanschay, two cities in the southern provinces of the Great Kingdom. Thousands of innocents lost their lives in the raids and conflagrations that scarred the towns.

Over the course of the war, thousands lost their lives. Yet a hero for the Great Kingdom emerged: Lady Kateri Shadowborn. One of the Ahltrian, a man named Lysander Greylocks led an ambush on the knights situated in Hammerlin, killing the majority of the knights but capturing a handful. As with previous atrocities, Ebonbane's domination caused Lysander to perform a number of horrible tortures upon them until the Grand Caliph ordered them to be brought in for interrogation. Kateri led the survivors to escape. The shoe was on the other foot two years later when Kateri defeated Lysander's troops and captured him at Sined Pass. With Lysander captured, Kateri detected the evil possessing him and freed him of it. With Lysander acting as advisor against Ebonbane's tactics, Kateri faced Ebonbane and banished it from the mortal world, including the Grand Caliph's soul. Unable to bear the weight of his actions under Ebonbane's influence, the Grand Caliph committed suicide soon after.

After his freedom from Ebonbane, Lysander Greylocks settled in at Forenoon Abbey in the Great Kingdom and became a monastic. A year passed and the Great Kingdom's armies, led by Lady Kateri Shadowborn, returned home victorious. Having become tired by war, Lady Kateri declared her retirement and returned to Shadowborn Manor, a home she had constructed in the south that was a replica of Shadowfast. The only three remaining Ahltrian, the Dark Triad, conjured Lussimar back into the world and put it into a magical sword. However, Ebonbane, as they called it, turned on them and slew them, reanimating them into its servants. Three years later, Ebonbane killed Kateri in her own home, drawing Shadowborn Manor into the Demiplane of Dread.

Note of clarification on the Great Kingdom

Note that the Great Kingdom of Avoneleigh is different from the Great Kingdom of Oerth. The matter is treated here: http://fraternityofshadows.com/forum/viewtopic.php?t=5389