Divergence

Seems to, generally, mark the end of The Second War
The "Calamity" was the final battles of the gods that directly preceded the Divergence

More detailed (but potentially biased) description of the event from Highbearer Vord:

"Dark gods" distanced themselves from the rest of the gods. They questioned the purpose of creation, and embraced the primordial chaos they once fought against. They taught mortals magic, Magic corrupted, and split people from the gods.
Then there was a sort of civil war, Arcane (Dark gods) vs divine (cool gods). This is the divergence. The gods and people fought against each other
Most cities fell, except Vasselheim. There was power up of the existing vestiges and more were created. Dark gods got banished to other planes. Also the gods thought they'd gotten too involved, and that was part of the problem. They peaced out, warning about the dangers of the arcane