Below is a condensed timeline of Matt Mercer’s Exandria campaign setting from Critical Role and related media. For a lot more detail, see the Critical Role Wiki.
Years are noted in relation to The Divergence (negative years before the event, positive years following it).
Mythic past … The Founding: Several gods (and/or The Luxon) conflict with chaotic elemental titans called Primordials. Exandria is given order and shaped. Mortals are created, after which the primordials attempt to destroy the new world. The gods split between Prime Deities (who defended mortals and order) and Betrayer Gods (who sided with the Primordials to return to chaos). Losers in this conflict are imprisoned until The Calamity.
-2,000 PD (approx.) … Age of Arcanum begins as mortals master the art of magic.
-665 PD (approx.) … Age of Arcanum nears its peak. Magic users learn to manipulate the flow of time.
-480 PD (approx.) … The City of Avalir atop Mount Ygora in Domunas breaks off and becomes a flying metropolis.
-310 PD (approx.) … A mortal mage usurps the God of Death and becomes The Raven Queen.
-290 PD (approx.) … The archmage Vecna, a native from the planet Oerth, becomes active on Exandria. Vecna draws many followers before retreating with them into the Shadowfell, possibly part of his multiverse-altering plan to achieve supreme divinity over the cosmos. (Vecna is also active in the Demiplanes of Dread/Ravenloft, Oerth/Greyhawk, Toril/The Forgotten Realms, and Sigil, the City of Doors/Planescape campaign settings prior to the events of Die, Vecna, Die!)
-190 PD (approx.) … The Calamity begins when the archmage Vespin Chloras and others unseal Asmodeus from his prison. Soon all Betrayer Gods are freed to return to the mortal world. Elemental rifts burst open across Exandria. War between gods rages across the mortal realm, destroying civilization and almost wiping out mortalkind. Only the first human city of Vasselheim (aka The Dawn City, The Cradle of Creation) on the continent of Issylra survives into the modern era. The continent of Domunas is shattered, leaving only an archipelago of scattered islands now known as The Shattered Teeth. The continents of Tal’Dorei, Wildemount, and Marquet suffer major topographical and climatic changes.
1 PD (approx.) … The Calamity ends when the Betrayer Gods are defeated at their stronghold of Ghor Dranas (now the modern Kryn Dynasty capital of Rosohna along the southern edge of the Barbed Fields region of Xhorhas). The Divergence seals all deities off from directly entering the mortal realm. Exandria’s ley lines are shifted.
After The Calamity … Mortals slowly recover and again settle across the continents of Tal’Dorei, Wildemount, Issylra, and Marquet. The Library of the Cobalt Soul, a religious/scholastic order, forms to rediscover knowledge lost during The Calamity.
445 PD (approx.) … The City of Ank’Harel is founded on Marquet by the mysterious J’mon Sa Ord. Around the same time, Zehir cultists seal the elder thing Uk’otoa under the ocean floor.
500 PD (approx.) … Archeologists increase study of relics found around the City of Ank’Harel.
725 PD (approx.) … Archeologists formally form a guild called the Allegiance of Allsight in Ank’Harel. Headmaster of the Crystal Chateau James Cryon is a founding member.
809 to 810 PD … A Briarwood noble is revealed to be a necromantic cult leader seeking to help Vecna achieve godhood over Exandria. Four dragons form the Chroma Conclave and prey upon the lands of Tal’Dorei. (Adventures of Vox Machina, pre-show and Critical Role Campaign 1.)
823 PD … Apex War fought in Marquet between the Stratos Throne and the Court of the Lambent Path.
830 PD (approx.) … Consortium of the Vermilion Dream society forms in Ank’Harel to collect and study an exotic red mineral called Ruidium.
835 to 836 PD … The War of Ash and Light fought across Wildemount between the western Dwendalian Empire and the eastern Kryn Dynasty. The conflict ends in a truce with little change in national borders. (Adventures of The Mighty Nein, Critical Role Campaign 2.)
837 PD … Rediscovery of the Jewel of Three Prayers in Wildemount. (Events of “Call of the Netherdeep” adventure.)
842 PD … (Adventures of Critical Role: Exandria Unlimited.)
843 PD … (Adventures of Critical Role Campaign 3.)