First Tymanther-Unther War

The First Tymanther–Unther War was a conflict between the nations of Tymanther and Unther that took place in the Year of the Rune Lords Triumphant, 1487 DR.

History
At some point in 1486 DR, while on the world of Abeir, the god-king Gilgeam contacted the demon lord Graz'zt and asked him to aid Unther in their war against the genasi forces of Shyr. Graz'zt provided Gilgeam with an army of demons to bolster his forces in exchange for powerful Abeiran magic items.

On Nightal 15 of 1486 DR, members of the Liberators of the Steel Sky accomplished the impossible and opened a portal to Abeir in the Catacombs of Djerad Thymar, believing they would save the dragonborn inhabitants of that world. However, one of the maurezhi granted to Gilgeam, whose mission was to infiltrate and debilitate the Shyran defenses, was accidentally sent to Toril through the portal. After killing all members of the Liberators, the maurezhi began to accomplish his mission on Djerad Thymar instead, eventually killing Vanquisher Tarhun on Nightal 25. The maurezhi was killed by Thymari defenders but, without a Vanquisher, Tymanther was left weakened against a potential invasion.

On Nightal 26, Unther was returned to Toril as part of the Second Sundering, and Gilgeam immediately moved against Tymanther to reclaim the former lands of Unther from the dragonborn. On Nightal 29, after having recovered the ruins of Unthalass and capturing dragonborn from Thymari homesteads and Lance Defenders scouts to gather enough intelligence about the Thymari defenses, Gilgeam launched an attack on Djerad Kethendi, officially starting the war against Tymanther. The Kethendan forward regiment was unable to defeat the demon army and was utterly destroyed. During the chaos of the battle, some of the Thymari prisoners, alongside a group of Untherite rebels who opposed Gilgeam, led by a military officer named Namshita, fled from Unthalass to warn the citizens of Djerad Thymar. Without their forward regiment, the Kethendans were forced to retreat to their city, and Gilgeam sent his forces and demons to lay siege to Djerad Kethendi.

As the Untherite forces advanced against Djerad Thymar and the Lance Defenders were unable to stop them, Yrjixtilex Kallan was chosen as the interim Vanquisher on Hammer 6 of 1487 DR in order to assemble all of Tymanther's military forces, and sent an unified front against Unther. After the new Vanquisher was elected, Namshita asked for political asylum for her and her forces in exchange for intelligence about the Untherite forces. As a preventive measure, members of Clan Shestandeliath used the Breath of Petron to raise an earth barrier around Djerad Thymar to protect the city.

On Hammer 10, the forces of Gilgeam laid siege to Djerad Thymar while the Chosen of the gods Asmodeus and Azuth conducted a ritual on the city in order to make both gods separate entities again. To maintain her position in the Nine Hells, Glasya sent the Malbolgean forces, led by a pit fiend named Khartach, to help the Thymari against the demons, helping the Chosen to accomplish their goal. As Asmodeus became an individual god by absorbing the divine spark of Nanna-Sin, he resurrected the former Untherite god as an immortal being. Grateful to the dragonborn for having taken care of him after the Spellplague, Nanna-Sin took the form a giant dragon turtle and went to protect Djerad Kethendi. He destroyed the Untherite navy, allowing the Thymari forces to lift the siege of the port city.

With the devils and dragonborn joining forces against his demon army, and the threat of the Second Sundering trying to return Tymanther to Abeir (a process that was stopped by the god Enlil), Gilgeam ordered his human forces to retreat to Unthalass. The demon army was completely destroyed, lifting the siege of Djerad Thymar and ending the war with a decisive victory for Tymanther.

Aftermath
After the war ended, Namshita and her rebel forces became Thymari citizens and Vanquisher Kallan allowed them to form their own clan, giving them full rights in Thymari society.

Although he was defeated, Gilgeam didn't relent from his plan to retrieve all of the former lands of Unther. As of 1489 DR, Tymanther and Unther were waging a new war, although the Untherite army was unable to defeat the dragon turtle that protected Djerad Kethendi. Mulhorand had closed its borders with the two countries because of the prolonged war.