None of the Great Maelstroms are minor events, but the Third Great Maelstrom was the one that shaped Stygian society into what it is today. The prelude to the Third Great Maelstrom was a sequence of social changes in Stygia, notably the Proclamation of Reason and the Breaking of the Guilds and an invasion of Stygia by Renegades around 1500 CE. The upheaval of the time expanded Renegade ranks as well as creating the Heretics in the first place. Stygia, in turn, turned inwards and the new factions of the Western Dead took this opportunity to exploit the age of discovery.
The Third Maelstrom took place in 1605, brought about by the destruction of the Flayed Lands by Heretic and Renegade factions invading the New World. The isolation and annihilation of an entire Dark Kingdom glutted Oblivion and caused a massive outflow from the Labyrinth. The response was so violent that it turned the Sea of Shadows into a permanent Tempest of violence and madness which isolated Stygia from the Shadowlands. In addition, the Nephwrack general Coldheart emerged from the Labyrinth and disrupted the River of Death; for the Maelstrom's duration, not even Ferrymen dared the river, instead using alternative byways.
The consequences of the Third Maelstrom were an almost total reordering of Stygian society. It sealed the division of Western society into Hierarchy, Heretic and Renegade factions, with Charon arming freewraiths and forcibly eliminating guild structures. Since that time, restoration of the guilds has been largely a fantasy of madmen like Lord Ember. In addition, it sundered Stygian power by forcing the Dark Kingdom of Iron to become a nation of cities - the first Necropolis was founded in London in response to the Maelstrom. It also increased the use of thralldom and soulforging in Stygia. Souls which were previously allowed to exist unmolested were now enthralled in the overcrowded Isle of Sorrows; Stygia's population problems would continue to trouble the Isle until the final Maelstrom. The demand for more durable Stygian Steel artifacts for Citadels and the need for more souls for byways led to even further exploitation of wraiths.