Timeline of the Sea of Dread

BC 7780: A subgroup of the Carnifex race from the city of Y'hog, and their troglodyte servants arrive in the Thanegioth Archipelago and the Serpent Peninsula. At this time, these islands lay closer to the northern Davanian coast. These islands are named the Va'ath-Zhemoth by the Y'hog Carnifex (DW, modified)
BC 7200: Concerned about the fate of their homeland, the Carnifex living on the islands abandon their palatial mansions, leaving most of their troglodyte lackeys behind, and ordering them to continue producing foodstuffs for the empire. (DW)
BC 7100: Shipments from the islands stop reaching Carnifex ports in Y'hegg-T'uhath and other regions completely. Concluding that the domesticated dinosaurs that guarded the farms had gone on a rampage and wiped out the troglodytes, the Y'hog Carnifex soon forget about the islands. (DW)
In truth, most of the troglodytes migrated to other lands, seeking true freedom from their Carnifex overlords. Many sail north to Brun, their descendants becoming the troglodytes known to most denizens of the Known World. Others sail south to Davania, offering their services as freemen to the Lhomarrians, who, desperate for more allies, accept. Others turn to piracy, while a fourth group migrates to the eastern islands in the archipelago, and try to build their own civilization, free from outside intervention. (DW)
Not long after their migration, the troglodytes are struck by a grim succession of calamities. Earthquakes destroy their colonies, eruptions burn their crops and poison whole villages with their fumes, and plagues of insects whittle away at the population. All of these things reduced the troglodyte colonists to barbaric Stone Age existence, reduced to one tribe living on Bararna Island, as their shamans seek an Immortal to guide them. (DW)
BC 6700: The troglodytes of Bararna Island are finally answered by an Immortal voice. It promises them the bounty of the seas, good hunting, and freedom from calamities. All it asks in return is total, unswerving obedience. Rejoicing at the prospect of being delivered from their personal hell, the troglodytes eagerly start worshipping this being, who was known by their former Carnifex masters as He-Who-Must-Not-Be-Seen, though he is named Gleesshka by his new worshippers. (DW)
Over the next centuries, the troglodyte population grows from a few hundred to several thousand. (DW)
BC 3100: Aquarendi elves seek the guardianship of Manwara, an Immortal of the sea, and enter the waters to begin a new life. (PC3)
BC 3000: The Great Rain of Fire; Blackmoor and Evergrun obliterated; the planet shifts its axis. Melting icecaps raise the ocean level by several hundred feet. The shark-kin return to the sea. (PC3)
Untouched by the cataclysm and isolated on the Serpent Peninsula, the Karimari tribesmen begin their rise to civilization. (CoM)
BC 2500: The Taymora humans settle the shores of the southern sea. (PC3)
BC 2300: The Sheyallia elves settle in the forests of the Serpent Peninsula. (CoM)
BC 2200: Tanagoro colonists reach the Serpent Peninsula and settle in the rain forests there. Conflicts arise between them and the Sheyallia elves. The Tanagoro keep to the coasts and lowlands; the Sheyallia move deeper into the forests, where they encounter the Karimari. (CoM)
BC 2100: Meditor and Verdier elf clans leave Ilsundal's northward migration and settle in southern Karameikos. (GAZ9)
One branch of the Meditor clan sails to a small, forested island just off the southern coast. There they build their home, which they name "Kal-Handir". The island is also given this name. (GC)
BC 2000: Series of great elemental upheavals split several large landmasses from the main continent. The Taymora civilization is destroyed. Meditor elves are left on the newly made islands in the Sea of Dread. (PC3)
Kal-Handir is miraculously untouched by the cataclysm. (GC)
BC 1750: Earthquakes in the Sea of Dread rock the Serpent Peninsula, flooding the central lowlands. The Tanagoro descend into squabbling tribes, and conflicts once again erupt between them and the Sheyallia elves. (CoM)
BC 1720: The landmasses split further, forming the Ierendi Isles. Primitive merrow enter the Sunlit Sea following the destruction of their homes to the south. (PC3)
Verdier elves build ships and join their cousins in the Sea of Dread. (GAZ9)
Remnants of the Taymorans, devastated by the continued destruction of what remains of their homes, attempt to conquer Kal-Handir, which has weathered the geologic upheavals intact. They are driven off by the elves. (GC)
BC 1650: Geological disturbances in the Serpent Peninsula settle, leaving it more or less looking as it does in modern times. (CoM)
BC 1500: Halflings from Davania pause in their northern migration along the Serpent Peninsula. They quickly move on. (CoM)
BC 1300: By this time a healthy trading relationship exists between Kal-Handir and the elves of Minrothad. Apart from this, the Kal-Handir elves shun contact with outsiders. (GC)
BC 1262: Urduk explorers make contact with the Karimari tribesmen of the Serpent Peninsula. (CoM)
Less than a decade later, the Karimari begin to make contacts with the outside world. (CoM)
BC 1100: Nithians led by Minroth colonize Trader's Isle and found Harbortown. (GAZ9)
A Nithian exploratory force is destroyed after it voyages too close to the island of Kal-Handir. (GC)
BC 556: Yav, son of a Tanagoro father and Sheyallia mother, is born. (CoM)
BC 529: A revolt breaks out amongst the Tanagoro of the Serpent Peninsula. (CoM)
BC 515: On Belissaria, a tribe of Yanifey, led by Ythol, their chieftain, decides to flee for better lands as the Alphatians continue to advance. He has his clan build great sailing ships, and they set sail westwards. Within weeks, they come across Kal-Handir. The elves refuse to let them land on the island, so the Yanifey decide to take it by force. Luck is with Ythol as his people manage, against all odds, to defeat the slightly less numerous elves. Some elves manage to flee to the Minrothad isles, where they settle amongst their fellow Meditors. Ythol is made king. Unable to pronounce the elvish name properly, he calls it "Colhador". (GC)
BC 501: Ythim, eldest son of Ythol, is crowned after his father's death. (GC)
BC 500: Yav, in the guise of Mulogo, proclaims himself herald of the Immortal Yav, and leads the people of the Serpent Peninsula on a migration to the Arm of the Immortals. (CoM)
BC 489: Yav leaves his people and returns to Thanegia Island. (CoM)
BC 475: Yav discovers an artifact of the Immortals beneath Thanegia Island and activates it. (CoM)
BC 472: Saloc assumes the throne. (GC)
BC 459: Hadlid begins his reign. (GC)
BC 425: City of Quagmire begins to sink into the sea. (CoM)
BC 410: Rikor assumes the throne. (GC)
BC 400: Yav reappears in Thanegia, having traveled through time. He journeys back to the Arm of the Immortals to check on his people. (CoM)
BC 383: Gorlab becomes king. (GC)
BC 354: Hador is king. His reign is far more illustrious than those of his predecessors are. (GC)
BC 339: Kordic takes power. (GC)
BC 329: Hadric, the first son of Kordic, is born. (GC)
BC 327: Meric, the second son of Kordic, is born. (GC)
BC 294: Through the practice of secret rites, Hadric becomes a velya. (GC)
BC 289: In a quake of tremendous power, Colhador sinks into the sea. A large section of the sunken city falls into a large crevasse. Hadric, in hiding for several years underwater, moves into the sunken city and begins to build up an army of undead, and he alters the ruins to his liking. (GC)
BC 200: Tritons fleeing from their devilfish enemies enter the Sunlit Sea and establish the Kingdom of Undersea in the waters between the islands of Ierendi and Minrothad. (PC3)
AC 0: First Emperor of Thyatis crowned. Thyatians trade with Minrothad islanders. (PC3)
AC 1: Yav appears, having traveled through time once more in his studies of the time artifact. He discovers that it is broken, and cannot journey into the past. (CoM)
AC 250: Alphatians found colony of New Alphatia on Trader's Isle; Alphatian magic is adapted to seafaring needs. (GAZ9)
AC 276: Human and elf cultures in the Minrothad Isles meet and establish trade. (GAZ9)
AC 284: Minrothaddan and Alphatian cultures clash on Trader's Isle over slave trading issues; elves force the humans to make peace. (GAZ9)
AC 300: The water elf trading port of Seahome is established. (GAZ9)
AC 360: Minroth traders carry slaves for the Thyatian Empire; halfling slaves are introduced to the Minrothad Isles. (GAZ9)
AC 400: The triton Tibaonisus prospers as a coral sculptor in Undersea. (PC3)
AC 410: Traders from Minrothad inadvertently spread the curse of lycanthropy to the kingdoms of Minrothad and Undersea. (PC3)
AC 443-445: Expeditions of elves and humans purge Minrothad Island of all lycanthropes. Similar events take place in Undersea, with many of the lycanthropes fleeing to deeper waters. This time is known as the Night of the Long Knives among merrow, and the Silver Purge among surface dwellers. (PC3; GAZ9)
Prompted by the lycanthropic plague, factions arise between the clerics and magic-users of Undersea disputing control of the realm. At the suggestion of their neighbors, the Aquarendi, it is agreed that only dual-classed cleric/mages will be able to rule the kingdom. The dynasty of the Farmarva family begins. (PC3)
AC 450: Malf Quickhand leads a halfling slave revolt; newly-freed halflings take ships and migrate to the island they name Open Isle. (GAZ9)
AC 475: The forest elf trading port of Verdon is founded. (GAZ9)
AC 488: Hadric Corser, the Great Uniter, brings the remaining humans together; founds the city of Minrothad, and lays the foundation for an organized trading federation. (GAZ9)
AC 494: The narwhal Eternal Voyager is born. (PC3)
AC 500: Conflict between Alphatian and Thyatian empires begins; Minroth traders maintain neutrality and dominate merchant shipping for both sides. (GAZ9)
AC 520: The halfling trading port and capital city of Open Isle, Malfton, is established. (GAZ9)
AC 570: First settlement started on Ierendi Isles by castoffs from the Five Shires. The islands are already inhabited by aboriginal peoples. (PC3)
c.AC 600: Lady Durnsay of Cathos leads her people in revolt against the vicious overlords of Vacros and their minotaur thralls. (M2)
AC 601: Gregus Verdier, the "Second Uniter," is born on Alfeisle. (GAZ9)
AC 646: Gregus Verdier has managed to forge the forest elves into a unified political and economic faction. (GAZ9)
Late 600's AC: Modern exploration of the Sea of begins, with the Kingdom of Ierendi and the Minrothad Guilds began competing in earnest (until this time, the Guilds had pretty much an exclusive on trade throughout the Sea of Dread; new opportunities in Sind and the development of the Ierendian Royal Navy helped fan the competition). (MyTh)
AC 691: Gregus Verdier establishes Council of Dread and the Minrothad Guilds. (GAZ9)
AC 700: Gregus Verdier is assassinated. (GAZ9)
AC 713: Ierendi Navy destroys a Thyatian naval patrol. The Royal Navy achieves instant preeminence among the powers of the Known World. (PC3)
AC 726: The Sindhi navy in Jaibul is destroyed. (It is widely rumored to have been due to the combined effort of agents from Ierendi and the Guilds, though there is little proof). (MyTh)
AC 735: Donatello "The Black" Matrongle, last legitimate member of the Matrongle line, disappears on an expedition to Davania. (MyTh)
AC 744: The sea giant Bratar is born. (PC3)
AC 748: The merrow of the Sunlit Sea agree to help the Ierendi Navy in return for Ierendi agreeing to protect sacred merrow shrines from pirate plunder. (PC3)
AC 750: Having finally fixed the time artifact, Yav reappears on Mystara, and returns to lead his people. (CoM)
AC 758: Yav retires from mortal life and ascends to Immortality. (CoM)
AC 791: The People of Yav uncover the ruins of the ancient city of Thanopolis, and begin to rebuild it. They call the city Tanakumba. (CoM, modified)
The triton Marcus (future baron of Souedge) is born. (PC3)
AC 800: Devilfish appear in the Sunlit Sea. War breaks out between them and Undersea, characterized by localized skirmishes and terrorist attacks by the devilfish. (PC3)
A volcanic eruption destroys the triton castle of Facats. (PC3)
AC 846: The triton Autalanus (future baron of Easa) is born. (PC3)
c.850 AC: An expedition that found it's way back after trailing off the west of the Strait of Dread returns with reports of a chain of islands, rich in ivory, gold and gems, but riddled with strange monsters and savage natives. (MyTh)
AC 852: Minrothad explorers, following a recently discovered map of Nithian origin, set off in search of the lost city of Thanopolis. They make contact with the Yavdlom city of Tanakumba. (CoM, modified)
AC 855: Tarovra Farmarva is born in Undersea. (PC3)
AC 860: An Ispan explorer, Don Sancho Estaban de la Villa Florida, of the Grand Duchy of Ispaņola, follows up on the Minrothaddan reports, and extensively explored the easternmost isle of the Thanegioth Archipelago. He names this isle Nueva Ispaņola in honour of his homeland. Don Sancho later follows up his initial expedition with further exploration, both of the Isle of Ispaņola and the other Thanegian isles. Eventually, a small settlement of a few hundred souls grows upon the northern shore of Ispaņola, and it becomes a revictualling station for explorers of the region. (MyNI)
AC 867: The kna Silvercrest is born. (PC3)
AC 875: During the era known as the "Years of Unrest", a time when the Thyatian Empire is battling rebels throughout their lands, many Ispan families decide to flee and seek their fortunes elsewhere. Eight score and eight ships leave the grand Duchy of Ispanola, under the leadership of Don Sancho, setting sail for Nueva Ispaņola. (MyNI)
AC 877: Haldo Waverider is born. (PC3)
AC 888: The triton Marseea (future baroness of Clarhars) is born. (PC3)
AC 890-913: Emperor Gabronius IV "The Conqueror" Tatriokanitas sponsors a number of expeditions to the Southern Continent, as well as several small colonies in the Thanegioth Archipelago. (MyTh)
AC 900: The colony of Nueva Ispanola is well established and its people have domesticated both the giant boar and the giant lizard. (MyNI)
Juliast Farmarva is born. (PC3)
AC 902: The triton Actonius (future baron of Trasar) is born. (PC3)
AC 910: The town of Puerto Segundo is founded on Nueva Ispanola. (MyNI)
AC 915: Puerto Margarita is founded on Nueva Ispanola. (MyNI)
AC 920: The war with the devilfish ends indecisively. (PC3)
AC 925: The triton Caxctiou (future baron of Calitar) is born. (PC3)
AC 935: The triton Claudia (future baroness of Werea) is born. (PC3)
AC 940: Three volcanic islands arise 50 miles off the southern coast of Aloysius Island. (PC3)
On Nueva Ispanola, the Western and Eastern Baronies are formally organized, with the leaders of the greatest of the local aristocratic families becoming barons. (MyNI)
AC 941: The triton Magdalene (future baroness of Soua) is born. (PC3)
AC 944: Hamish McGregor is born. (PC3)
AC 950: Tarovra Farmarva becomes Queen of Undersea. (PC3)
Nueva Ispanolan trade with Minrothad picks up, helping to spur the growth of the plantations further into the jungles until the current border is reached (in the 970's). (MyNI)
AC 979: Devilfish resume their attacks on Undersea. (PC3)
AC 980: Lycanthropes are again discovered in Minrothad and in Undersea; fear spreads that the devilfish might be responsible. (PC3)
AC 988: Thincol I Torion, seeing potential in the lands of Davania, began an official Imperial Colonisation Program of the southern continent. (MyTh)
Emperor Thincol initially he feels it would be simpler to conquer Nueva Ispaņola than to deal with the proud Ispans. However his magist Demetrion successfully dissuades the Emperor from any such action, pointing to the Nueva Ispanolan's longstanding treaty with the kingdom of Twaelar. (MyNI)
AC 998: Undead reported in the waters to the south of Undersea. (PC3)
AC 1000: Shark-kin tribes take up arms against the land dwellers; devilfish increase their attacks on Undersea; the numbers of undead and werecreatures in the southern waters grows at an alarming rate. (PC3)

Sources

CoM: Champions of Mystara boxed set, DM's guide.
DW: Geoff Gander's "Dark Worship in the Known World" article.
Gaz9: The Minrothad Guilds gazetteer.
GC: Geoff Gander's Colhador timeline.
MyNI: James "Mystaros" Mishler's gazetteer of Nueva Ispanola.
MyTh: James "Mystaros" Mishler's history of the Thanegioth Archipelago.
PC3: The Sea People