Time of Troubles

The Time of Troubles, also known as the Arrival, the Godswar, and the Avatar Crisis, was a cataclysmic time period in the chronology of Faerûn. Taking place nearly 200 years, the Time of Troubles was a period during which the deities of Faerûn were forced to walk the earth in their mortal avatar forms. Several major deities died during the Time of Troubles and a handful of mortals rose to divinity.
The Time of Troubles was precipitated by an attempt by the god Bane to steal the Tablets of Fate from The Overdeity Ao. Angry at the gods for their habitual pursuit of power and negligence toward their mortal faithful, Lord Ao relegated every god (except for the guardian god Helm, selected to protect the gates to the heavens) to walk among their followers on the earth. The immediate effects of this edict were threefold. First, divine magic ceased to function altogether unless the cleric was within one mile of their deity's avatar. Second, arcane magic ceased to be regulated by its steward, Mystra, and became dangerously unpredictable. Third, the characteristically immortal and aloof deities were now vulnerable (though still devastatingly powerful) and dwelling among the civilizations of Faerûn.