I'm surprise Nightstalkers didn't recommend this:
www.phyrexia.com
A great resource for finding out about the stories.
It is very hard to give an brief overview of the world's events in Magic. There are so many characters, side events, and great wars that things are rather huge to summarize.
World events are like this, in total watered-down summary:
-Dominia is a multiverse of many planes.
-Dominaria is the main world in this multiverse. Two times the size of earth, with supercontinents and much ocean. It has two moons.
-Thousands of years ago, tw brothers, Urza and Mishra, became powerful wizards and fought in a cataclysmic war, which destroyed lands and changed the climate of the world.
-Urza killed Mishra, and also journeyed to the worlds of Phyrexia (which was an evil demon/zombie-like place that was later learned to be planning a plot to take over Dominaria) and some angel realm controlled by Serra. At this point, Urza was a planeswalker, equal in power to a Player in the game (thus he is not a creature card).
-With the global climate ruined, and the world went into a huge ice age.
-The ice age was cleaned up by the goddess Freyalise and things began to go back to normal, though with much casualty across the world, and with a drawn-out Dark Age afterward.
-Fast-forward to what was the "modern day" for years in the game, the crew of the airship Weatherlight became involved in stopping the Phyrexian plot to take over Dominaria, by traveling to the planes of Rath and Mercadia, which were friendly to Phyrexia in the takeover mission.
-When the Weatherlight returned to Dominaria, with a few losses in crew, they were a sort of flagship in the Phyrexian invasion.
-The cultures of Dominaria, vast and longtime enemies with each other, allied in a Coalition to resist the Phyrexian invasion, which included "overlaying" sections of the world of Rath on top of parts of Dominaria, as well as world plagues that ravaged populations.
-Ruthless, savage, devastating combat ensued, and the world was left in total ruin. Minimal survivors, and lost empires and extinct species were the result of the eventual Coatlition "victory" over Phyrexia. Yawgmoth, the leader of the Phyrexians, was killed. But not after Urza (who was a planeswalker and thus lived a long time) was killed by Gerrard in a mind control fight staged by Yawgmoth. Gerrard was killed in the Weatherlight attack on Yawgmoth's fort. Apparently, they harnessed the power to cause one of the world's moons to slam into the fort and obliterate it.
-Karn, a golem made by Urza, and crew member of the Weatherlight, became a planeswalker.
-Fast forward 100 years, the continent of Otaria, one of the least affected regions of the world, slowly recovers from the war's destruction and the first bits of civilization form, centralizing around gladiator combat.
-The Cabal, a corrupt crime organization, finds the Mirrari multiple times and launches the continent into frenzied competition over the powerful metallic orb.
-After wars for the Mirrari and countless deaths, even a change to the continent of Otaria itself, a barbarian named Kamahl attains the Mirrari and it fuses itself with his sword, which is said to be made from the metal of Urza's magical staff.
-Kamahl fights his sister, Jeska, and nearly kills her. He begins a journey to the forst to find a way to stop the violence caused by the Mirrari, which has maddenning powers that turn its wielder into a destructive maniac. Jeska is captured by the Cabal, and turned into the evil fighter Phage, who's touch can melt any organism.
-Phage fights a wizard named Ixidor and his fiance in the pits. She kills Ixidor's fiance. Ixidor, stricken with grief, uses his powers to craft Akroma, an angel copy of fiance, and powerful warrior for his maddened vengeance.
-Phage and Akroma, in an army-vs-army standoff, try to kill each other but merge into one being, Karona.
-Karona tours Otaria in search of her meaning, but her allure and awe cause hordes to follow her and kill each other over her. She eventually goes mad and is killed by Kamahl's sword with the help of some of Ixodor's former minions.
-The death of Karona reveals Jeska, as a planeswalker, and she leaves Dominaria to meet Karn in the world of Argentum.
-Karn and Jeska go planeswalking together and leave the Mirrari, turned into a warden, to watch over the barren plane of Argentum.
-The warden becomes Memnarch and turns Argentum into Mirrodin, covering the metal world in life that absorbs the metal, by robbing organisms from other planes.
-Thousands of years later (perhaps 10k), an elf named Glissa discovers the inhabitants of the world have been abducted and brainwashed to populate Mirrodin.
-Glissa kills Memnarch and returns all organisms to their former homes.
-Glissa, the necromancer Geth, and Glissa's friend the goblin Slobad, are the only life forms left on Mirrodin, set to wander Mirrodin but with the ability to go back "home" should they ever choose to.
And at that point, we find the story as it closes at Fifth Dawn. With Kamigawa block, we shall see what a new world is like, and perhaps in a future set, we shall see what happened to Dominaria in all those thousands of years to rebuild after the Apocalypse.
I hope this helped.