Is there an overview somewhere of what changes were made to the Realms for 4e, and why they were made? It sounds interesting, but I only understand snippets here and there.
I will say that rolling back the changes led to some of the less convincing parts of the SCAG - endless rainfalls and whatnot.
This might be helpful:
http://forgottenrealms.wikia.com/wiki/Spellplague
By comparison, this is the greater part of what the Sundering brought:
[sblock]Sources: the Sword Coast guide, Ed's answers, various novels. The Sword Coast guide doesn't really explain how the changes happened. It just says ''the Sundering happened, and this is how the FR and its pantheon look like now'').
The Sundering basically consists of Ao rewriting the tablets of Fate, bringing back many gods, and separating Abeir and Toril again.
By rewriting the Tablets of Fate, Ao seals the various gods power and portfolios and establishes new rules to avoid further divine conflicts and the cataclysms that they brough (in fact the gods are supposed to be more distant now).
The various deities invest power in mortal chosen, trying to expand their influence before Ao could finish rewriting the tablets. However this gamble goes badly for most deities, except for a *large* group of deities that people believed gone, but that actually managed to return thanks to Ao (and other contingencies, in some cases), mostly to how they were in the 1370s DR. Most of those chosen are no longer such as of the 1490s, as their deities have withdrawn their power.
Cyric no longer is the god of murder, Bhaal returned claimed that portfolio, Myrkul returned and claimed the portfolio of death, while Kelemvor currently is the judge of the dead. Leira and Mask also returned (Mask has returned through the ascension of Drasek Riven, though), so Cyric mainly is the god of lies now.
Other deities that have been restored are Helm, Tyr, and Azuth (we know that the latter is back, but that story isn't complete yet). The elven, dwarven and halfling pantheons are back to how they were. The drow pantheon is back too, with the difference that Eilistraee and Vhaeraun are no longer enemies now, and might be working together. Eilistraee in particular has personally appeared to mortals, and seems to be trying to build stronger relationships with other races. She has manifested near Waterdeep, and now her followers are building a glade/temple within its walls, to replace the fallen Promenade.
About Shade/Myth Drannor: during the Sundering the Shadovar attempt to kill the various chosen created by the gods and drain their power. They also attempt to drain the mythal of Myth Drannor. Larloch also attempts to drain the mythal and the wards of Candlekeep, in order to become a god. Elminster, Storm, Alustriel and Laeral and the Srinshee battle at Myth Drannor against Larloch and the Shades (these two are not allied), to protect the Weave and the elven city (yes, Laeral and Alustriel are alive: Khelben had foreseen all the mess of the Spellplague and various cataclsysms and had ordered Laeral to prepare to prevent the Wards of Candlekeep from being used by ill-intentioned individuals. Larloch however managed to absorb them as a part of his plan to ascend to godhood). Chaos ensues: the Srinshee sacrifices to take the energy that Larloch had drained from the wards and infuse it in the Weave; Elminster kills Tanthul and Shade crashes on Myth Drannor, severely damagin the city, but not destroying it. Currently most elves are in Semberholme and other settlements, with a little community still in Myth Drannor, gathered around the Tree of Souls (which was saved by a group of Baelnorns who had been informed of the imminent cataclysm by the Srinshee. Those balenorns are still there, guarding the Tree).
Other major events, mostly regarding geographic changes are:
-The Plaguelands are ''healed'' , the Earthmotes fall, the Sea of the Fallen Stars reforms, the Underchasm is filled.
-In Waterdeep downshadow is abandoned, and Laeral becomes open lord.
-Mulhorand and Unther return from Abeir, and so do their deities (the Mulhorandi ones rule as avatar; in Unther, even Gilgeam and others who had ''died'' long before the Spellplague returned. Apparently a reincarnated Gilgeam guided his people on Abeir). However a part of Tymanther remains, albeit the dragonborn have been driven away by the returned Untherites, whose goal apparently is to completely wipe what remains of Tymanther and the dragonborn civilization.
-Maztica is also back. Or seems to be.
-Evermeet currently touches three planes: Toril, the Feywild and Arvandor, and can be physically reached from Toril (as in, you can go there with a ship).
-Halruaa managed to shift to Abeir before the Spellplague, and now is back.
-Lantan re-emerged, but most of the gnomish wonders are gone.
-Luiren is no longer flooded.
-IIRC, at some point during the Sundering, there was a movement of living Red Wizards that was trying to take back Thay. I don't know what happened to them, but I guess that their efforts led to the situation described in the Sword Coast Adventurer's Guide (i.e. the living can advance in rank within the Red Wizards).
I guess this is all. There could be mistakes, so correct me if I'm wrong.
This might be of help:
http://forum.candlekeep.com/topic.asp?TOPIC_ID=19630[/sblock]