I believe you have tackled one of the hardest of the two things in campaign world development - the history/theology. I understand it, it's easy to grasp, and Joe Average Adventurer won't have a clue as to the who/how/why, but the PLAYER will get it. To me, you have tiger blood here... WINNING!!!
Now, the next hard part. Geomorphology.
First question: What kind of nukes were used? Neutron bomb type (lots of short-term radiation and little structural damage) or old-fashioned dirty fission/fusion bombs that left stuff dirty for a LONG time and destroyed large areas? Figure this out, and you can start to make changes in the geology. If London was hit by several "dirty" bombs, it may be a lake, now, but Bristol is pristine after being hit by neutron bombs. How many areas are STILL too radioactive to visit, and get specific about exactly where they are and what happens with things that visit.
Second question: How long ago was this? Did the nukes get the continental plates to shift? Did the resultant radioactive cloud create a new ice age? The Ring of Fire may have created whole new land masses, and entire mountain ranges may have been suddenly created by the sudden movement of plates. Other ranges may have been ground down to nothing by resulting ice-sheets.
Last question: Are there ANY pockets of pure HUMANITY left that are untouched? How might they react to D&D-land encroaching on their lives?
All in all, I REALLY like what you've done. Keep it up!!! Oh, and keep us POSTED!