The Calamity

The Calamity was the second war against the Betrayer Gods, which devastated civilization and in some cases rearranged the geography of Exandria. The exact year when the war started is unknown; it brought about the end of the Age of Arcanum, and concluded with the defeat of Tharizdun, the Chained Oblivion and the construction of the Divine Gate.

Divine warfare
Following the release of the Betrayer Gods by Vespin Chloras, the establishment of their kingdom of Ghor Dranas, and their assault on Vasselheim, conflict against the Betrayer Gods was rejoined. In general, the inability of the Betrayer Gods to work together allowed them to be defeated, though for a brief period there was unity between the Demon Princes for the purposes of fighting the Prime Deities.

Both deities and archmages crafted legendary artifacts during this period; many of these Vestiges of Divergence are buried or lost, but some have been recovered.

Lolth was one of the earliest casualties of the Calamity, as Kord impaled her with a thunderspear before her soldiers saw battle. Over the years, her most loyal drow servants discovered her pooling blood and drank it, transforming themselves into half-spider hybrids called driders. The leaderless drow were driven from the surface world and had to rebuild in the Underdark; their nobility began to be influenced by Tharizdun.

The sequence of some events can be put in order:
 * Torog and his followers tunneled beneath a woodland in the Cyrios Mountains that was home to reclusive elves who worshiped Sehanine, sinking the plateau into a valley. Torog's servants sapped the life and color from the trees at their roots, creating the Pallid Grove.
 * Moradin and Sehanine built the King's Cage as a trap for Torog. It appeared to be a temple to Torog, but it was a fane that, once Torog had bound himself to it, was instrumental in banishing the Betrayer God.
 * Pelor and Sarenrae drew Torog above ground, defeated him, and banished him to a sliver of the Far Realm that now borders the lowest depths of the Underdark. Torog's tears burned tunnels through Exandria, and his faithful fled into them.
 * Asmodeus deceived and betrayed Sarenrae, and killed most or all of her worshipers, in one stroke.
 * The original Cerberus Assembly tore Desirat, phoenix mount of Asmodeus, from her master and bound her beneath Mount Mentiri for study.
 * Avandra defeated Asmodeus by tricking his armies into fighting each other.

Other battles are harder to place.
 * All the deities momentarily struck an armistice to strike down the flying city of Aeor, which had developed weapons to kill gods, and the gods' combined might managed to crash but not destroy the city.
 * Clemain Astural, a powerful arcanist, looked into a realm beyond the planes for the power to end the war, and he got the power but lost his sanity under the influence of an entity he called the Sightless One. He devastated southeastern Gwessar before heroes brought down his tower and killed him.
 * In one famous battle, said to occur on the hill that would be named the Throne of the Archeart, Corellon battled Gruumsh, stabbing out his eye.
 * At some point, in what would become the Greying Wildlands, Corellon's right hand, the solar Xalicas, was so badly injured that she could not see, fly, or leave Exandria, and had no strength to move for over a century.
 * Zehir ambushed and killed many followers of Melora in the area that became the Lushgut Forest.
 * One of the bloodiest battles of the war took place at the site where Bladegarden would be established, leaving behind a vast amount of weaponry.
 * The Raven Queen's black-winged angels saved her from a near-fatal run-in with Tharizdun, but were all consumed in the process.

One of the climactic fights of the war came about when the Prime Deities sought to banish Tharizdun. Moradin used the Core Anvil to craft the Prime Trammels used in the Rites of Prime Banishment. Ioun baited Tharizdun to her central temple, resulting in her near-destruction and causing her temple to sink beneath the earth in her sorrow. With the blessing of Avandra, four Prime Trammels were attached to Tharizdun, and Pelor prevailed in a battle with the mad god. Badly defeated and wounded, Tharizdun retreated to Acek Orattim's realm, but Pelor chased and banished Tharizdun there, beneath Gatshadow Mountain.

In one of the last battles of the Calamity, Melora and her Free Children battled Bane and his goblinoid legions, this time on the Beynsfal Plateaus of the Rifenmist Peninsula, where Bane was defeated and his armor was scattered across the region.

The final battles of the Calamity took place in the valley that would become the Barbed Fields. Some champions of the Betrayers were trapped afterward:
 * Quajath, who had acted as Torog's scout, was thought to be slain, but it burrowed deep beneath Eiselcross and got stuck there.
 * The body of Jourrael, Lolth's chosen assassin, was split into pieces and sealed in separate secret locations, for lack of a way to kill her.

Attempts by mortals to flee the war
Just before the war, followers of Zehir slaughtered the people in the Vault of Shumas and locked it off. An undead caregiver there watched over the sleeping children of Zehir, awaiting their epoch. Similarly, seers of a serpentfolk empire foresaw the Calamity; to survive its dangers, the empire created a magical stasis field under their capital city of Vos'sykriss (now Visa Isle) where its strongest people waited to one day emerge and rebuild their empire.

In the Ashkeeper Peaks, the dwarven clan of Grimgol was almost wiped out; the survivors burrowed deep and collapsed the established tunnels to buffer against the wars above, and so began centuries of isolation.

Almost all elven civilization disappeared from Exandria during the Calamity. A wandering colony of elves fleeing the Calamity formed the beginning of what would become the Orroyen tribes of the Rifenmist Peninsula. The elves of the fallen Court of Ullusa sought shelter in the Feywild and only returned a generation later, eventually settling in the Verdant Expanse. After Corellon's battle with Gruumsh, the elves of northern Wildemount, pleading to Corellon for protection, heard no answer, and encased their civilization in ice and fled into the Feywild.

The Sehanine-worshiping elves whose home was transformed into the Pallid Grove retreated underground, beneath the Grove, and became pallid elves. Elsewhere, entirely new races were created by the war.

New races
The evil god of war and conquest, Bane, transformed many of the Dranassar into goblinoids to fill different roles in his armies, and left them burdened with the Curse of Strife.

As an unknown deity entered Exandria to do battle, a pack of wild hyenas were caught in the divine eminence and became the first gnolls.

Creation myths hold that when Corellon stabbed Gruumsh, the fallen blood of Gruumsh mutated a number of elves into orcs, and other fallen elves who had fought alongside Corellon were raised and fused with their horses, creating centaurs. The first half-orcs in Wildemount were born in the final days of the Calamity.

When Tharizdun was banished, the Raven Queen's angels he had consumed returned as diminished, mortal kenku.

Reshaped geography
Across the world, the forces unleashed by unrestrained divine and magical warfare left permanent scars on the land itself.

Some of the most terrible battles of the war reduced the battlefields to ash. In the early years of the Calamity, warring nations in Marquet turned the verdant landscape into ash and desert. Incanter's Rest in Blightshore is so blasted, it's unclear whether it was the site of the biggest battle ever to hit Wildemount or the site of multiple battles. Toward the end of the war, the site of Melora's final battle with Bane was reduced to ash, and plants wouldn't grow there ever again. And in the end, the kingdom of Ghor Dranas was itself turned to ash, and the Barbed Fields are a treacherous land pocked with sinkholes and tar pits.

The once-tranquil coastal paradise of the Miskath Strand was defiled by the Betrayer Gods and became the dramatically transformed Blightshore.

The aforementioned creation of the Pallid Grove was not the only forest transformed by the war.
 * When Zehir ambushed Melora's forces, her screams created the choking Lushgut Forest.
 * What became the Crystalsands Tundra is said to have once been a continuation of the Veluthil Forest until a battle there smashed everything.
 * Less than a century before the war ended, an extremely slow-burning arcane forest fire started in what later became the Greying Wildlands, and was not extinguished until after the Calamity ended.
 * The Saltwallow Bog is said to be toxic as a result of a servant of Torog's corpse having fallen there.
 * Jungles reclaimed the Menagerie Coast and Swavain Islands after the civilization there was swept away by the surging sea.
 * The shift in ley energies following the Calamity created a surge of growth that created the lush Verdant Expanse in a place untouched by the Betrayer Gods.

The land bridge connecting Gwessar (later called Tal'Dorei) and Wildemount was shattered, creating the Shearing Channel. Considering the proximity, this may or may not have happened in Pelor's vengeful battle against Tharizdun, which was so violent that it created the valley where the Parchwood Timberlands stand and raised the Alabaster Sierras.

The final battles of the Calamity left particularly large scars.
 * Xhorhas, once densely forested, became a blasted wasteland.
 * A section of the nearby Ashkeeper Peaks and Dunrock Mountains was shorn flat, creating the Brokenveil Bluffs and the passes on either side. This may be when the mountains the dwarven clan of Grimgol had called home were destroyed.
 * The final battle of the Calamity sent strong waves of magical force through Exandria, unintentionally causing the collapse of most of the Crystalfen Caverns and the fall of the aberrations' civilization there.

Fates of mortal cities
All the flying cities were wiped out, as far as anyone knows. At least three crashed in Wildemount: Aeor in Eiselcross, Zemniaz in the Zemni Fields, and Kethesk in the Dreemoth Ravine. Aeor was struck down well before Zemniaz fell. The city-state of Draconia was established in the Dreemoth Ravine out of an alliance between the native ravenites and the foreign draconbloods.

The dwarven kingdom of Uthtor was destroyed, and as mentioned above, the dwarven Grimgol clan was nearly wiped out. Other dwarven strongholds in the Ebonglass Massif, including Xagonstar, were completely destroyed.

The people of Vos'sykriss who were not chosen to go into stasis were killed off in the Calamity, and some still haunt Visa Isle as ghosts.

The final battles of the Calamity caused massive floods and tidal surges that swept all civilization from the Menagerie Coast and islands of the Lucidian Ocean.

The collapse of the Crystalfen Caverns brought about the immediate fall of the aberrations' civilization that had been centered on Salar. The earthquakes caused by the war are also said to have caused a temple to sink beneath the Ounterloch.

Most cities that had sprung up during the Age of Arcanum were reduced to ash, leaving Vasselheim once again as the sole bastion of civilization. Historians estimate that no more than one-third of the world's population survived this war.

The Divergence and other consequences for the gods
In the end, the kingdom of Ghor Dranas was defeated and the Betrayer Gods banished once more, but now with the knowledge and fear that they could return again. While the mortal world recovered slowly from the devastation it had endured, the Prime Deities were left to ponder how they might prevent a third divine war. Hoping to seal away the Betrayer Gods for good, the Prime Deities retreated from the Material Plane. Behind themselves and their defeated brethren, they erected a barrier known as the Divine Gate, which would prevent any god from physically crossing over into mortal realms. The departure of the gods from Exandria, and the diminishing of their influence, was an event that has since come to be known as "The Divergence", though it goes by other names.

There were further consequences for some gods. As already mentioned, Sarenrae's worshipers were either mostly or entirely wiped out. Lolth lost her influence over the drow of Wildemount, who largely turned to the Luxon. Most of Zehir's worshipers were destroyed. Ioun's public worship was shattered; her following was largely culled. And more than 800 years later, Ioun was still recovering from the wound Tharizdun had given her.

Trivia

 * Mages and followers of the Betrayer Gods used gloomstalkers as mounts during the war.