Could my Answer be in the Realms?

I am moving my 3.x game over to a 4e one soon.    I have been buying up the Essentials books and some modules and I generally have what I think is a cool idea for campaign.  The world is fleshed out and I know what I am going to use and what I am not.

Except there is one little-bity problem. So much of what was true in my 3.x world no longer "works" under 4e.  Or rather it works so differently now that it is hard to see it working the same way when I was playing 3.x.  Then there are other issues.  My kids want to play the children of their D&D 3.x characters and these characters have some serious magic.  And there is the whole killing Tiamat thing they want to do.   How do I explain the changes?

Turns out the answer was under my nose this whole time.  In the Forgotten Realms Player's Guide.

I was never a fan of the Realms.  I considered it to be a pretender to Greyhawk and not a very worthy one at that.  I picked up the 3.0 Realms Guide when it came out and I liked it.  I felt it was a good book and all it really was missing was monsters.  The new 4e campaign books are a good model too.

But what I like the most about the Realms book is how completely gonzo it is.  Smash two planets together to get one world! I love that!  Spell plagues? Bring it on!

I know I have talked around all of this before in many posts, but it is time to make it more real I think.

So what will I include from the Forgotten Realms book in my Game World?

First, well, it is going to be in the future.  I am going to say about 25 to 30 years.  Not 100% sure, but long enough to have the world changing events happen at least a generation ago.  The Characters of this game have only know the world as it is now, never the world before.

Next, there will be a Spellplague.  The defeat of Tiamat and the Ascension of Asmodeus are just parts of that.  I am also going to have Raven Queen in my game and she just killed Nerull.  There will other things of course, but it was a series of Cosmos-shaking events that left the world changed.  The Fey-wild is now easier to get too, as is the Shadowfell (previously only known as the Plane of Shadow).  The main effect for the PCs is that some of the old magic no longer works.  So there is a quest for sources of "Old Magic" or even "True Magic".  With this, some older magic items are now useless.  Of course the spellplague was chaotic so some normal items are now magical.  There is still magic to be found out there "New" and "Old".
Living things touched by it have been altered.  There will be spell scarred.

The ancient Astral empire of the Tieflings, Bael-Turath, has crashed into the world.  Here I am taking inspiration from the 90's TV show "Alien Nation".  Though this is a "magical crash" so there are now lands where there are ruins of the Tiefling society that seem ancient and always part of the land.  Bael-Turath had warred against Asmoedeus and the devils for countless centuries.  Part of Asmodeus' ascension was to reclaim the power that emperors of Bael-Turath had stolen from the Nine Hells.  The tieflings are now a broken, homeless race with members now fond all over the world and many still in the Astral Sea.

The Blood War is over.  With Asmodeus' Ascension and the Reckoning of Hell, the long war with the demons is over.  Asmodeus even managed to conscript entire demonic species under the auspices of Hell.  With the the power he gained Asmodeus broke the paths through the Astral that the demons and devils used to attack each other, effectively blocking demons from being able to enter the Prime Material.  If a demon wants to get to the Prime Material plane it has to go through Hell first.  By the time of the new game the distinction between "demon" and "devil" is a loose one in most peoples minds.  Plus the entire race of yugoloths were sacrificed in the process, with many seeking refuge in either the Abyss or Hell.
Asmodeus covets the Material World and wanted to bring Hell into it.  Here he failed, but managed to get it much "closer" metaphysically speaking.

One repercussion of this though is demons now focus on the Prime Material.  While it is harder for them to reach it now, many still do and with out the Blood War to contend with it is possible that more demons than ever are now attacking mortals.   This is something Asmodeus wants.  He has placed members of his cult in areas to fit demons and rally humans to his cause.  As the game progresses the influence of this cult will be more readily felt. To combat this the Gods will be using the mortal realm as their battlefield.

I think this is a good start and gives me a good idea of what my end game needs to be too.  Lolth, in one form or another will have hand in all of this too.  Events that began in my Shadow War of 1st Ed are now coming to a head.

Now I need to figure out who the main bad guys are and what they want to get out of all of this.