20 Olarune 994 YK, the Day of Mourning, marked more than the beginning of the end of the Last War, it was the end of a nation. On that day the nation of Cyre was destroyed in a holocaust of fire and magic.
In what is now known as the Field of Ruins in southwestern Cyre, the combined forces of the Brelish military, led by Princess Borann, and Thrane armies, led by Bishop-Militant Grodan, a close friend and advisor of High Cardinal Krozen, joined by pact, were attacking a much smaller Cyran force. The Cyrans had just been reinforced, after having cleverly used tireless warforged units for days to convince their opponents that they possessed greater numbers, but were still outnumbered 3-1.
However bad things might have looked for the Cyrans, no one could have imagined the devastation in store. And the invading armies were not spared. The skies are said to have burned so brightly that soldiers at Angwar Keep in Thrane were blinded. In the end, virtually everyone within the borders of what is now the Mournland perished.
The Forge of War. James Wyatt, Wolfgang Baur, Ari Marmell (2007). Wizards of the Coast. ISBN 0-7869-4153-7. Sharn: City of Towers. Keith Baker and James Wyatt (2004). Wizards of the Coast. ISBN 0-7869-3434-4.